adds update app feature

[zimbora]

Wallet update

How to use it:

• Launch app with arg "-update"
• Use UI app to update the wallet

How it works

If "-update" arg is received, software will check the latest version. If a new version is available it will download, create a backup and run it.
If update is requested through UI, the app will restart with "-update" arg.

Wallet UI

If a new version is available an icon will appear on topbar and for the first time that a new version is detected a dialog window will be shown to the user.

Method:

• Release is downloaded from github DSW repo using github API.
• SHA256 is compared between the dowloaded zip file and github file.
• File is unzipped to the location where the program is, current directory is changed if needed and the program will restart again with the same command but without args.
• All executable files are replaced with new ones.