Refine directory structure and management

[skaldarnar]

Launcher Data

The launcher is "installed" in some directory (currently by unzipping the distribution archive, installers are planned in #520 ). All files and resources to run the launcher are contained in this installation directory.
The game(s) will also be downloaded to and installed in this installation directory. The user can chose the launcher installation directory (currently by extracting the ZIP or moving the extracted folder, later by choosing the installation path in the installer).

Game Data

The actual installation of the game, e.g., a downloaded and extracted Omega ZIP archive. The launcher manages different game installations within the game data directory and provides means to open that directory from the launcher. The user cannot change the directory.

User Data

Configuration files and settings that can be customized by the user. On Windows, these can often be found in <User>/AppData/Roaming/Terasology, on Linux system dotfiles in the user's home directory are common (e.g., ~/.terasology).
This also includes settings and user-specific files of the game(s) itself, such as customized keybindings or saved games. On Windows, we will continue to store saved games in Saved Games folder. For now, this corresponds to the -homedir option of Terasology.

Target Architecture

• We no longer treat the game and the launcher as separate applications with their own directories.
• Application Directory: contains launcher data and game data. The installation directory of "the game and its launcher".
• User Directory: external directory for user data, as described above.

The launcher MUST allow the user to open the user data directory from the settings menu.
The launcher MUST allow the user to open the launcher installation directory from the settings menu.
The launcher SHOULD allow to open the user data directory for a specific installed game (possibly via an additional button next to Play and Delete).
The launcher MAY allow to change the user data directory through the settings window. This would include to move all existing settings.

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v4.0.0 TODO:

• disable the option to change the user data directory (feat: cleanup and clarify settings #503)
• disable the option to change the game data directory (fix: small adjustments in settings view #537)
• merge game data directory into the launcher installation directory as Application Directory (feat: merge 'games' directory into launcher installation directory #536)

v4.1.0 TODO:

• have separate user data directories for individual games
• add button to open user data directory for currently selected game
• move existing settings on changing the user data directory

Closes #340

[jdrueckert]

We did not mention the .terasologylauncher (Linux) directory.

1. We should discuss the platform-specific differences with respect to merging this into the .terasology (Linux) directory.
2. Are all three folders "cache", "download" and "temp" necessary?
3. Why are the downloaded game .zip archives put into "cache"? I'd thought that's what "download" is for...

[skaldarnar]

@jdrueckert The ~/.terasologylauncher is implicitly mentioned in the issue as user data/user directory. The important sentence for the target architecture is:

We no longer treat the game and the launcher as separate applications with their own directories.

To me it's not completely clear how to treat Windows systems here, as they have Saved Games and AppData as separate concepts. My initial guess is that Saved Games corresponds to -homedir option of the game, and AppData contains configuration files, settings, etc.