Make the toolbar customisable

[politas]

Different users have different requirements from CKAN. Users who want to play around with multiple installs will frequently want the "Select KSP Install" functionality. Those of us testing metadata make a lot of use of the "Install from .ckan" functionality. Some users, (like myself) never, ever use the "Launch KSP" button.

I propose we add toolbar buttons for most menu options, and a "Customise Toolbar" dialog allowing users to add, remove and rearrange the buttons on the toolbar.

This suggestion comes out of the conversation on Issue #1638

[HebaruSan]

The recent trend in UI design seems to be toward somewhat less in-depth customization. Modern apps have settings, sometimes lots of them, but usually not at the level of pre-"ribbon" MSOffice with adding/removing/rearranging whatever you want however you want.

If we make a new UI (see #2848), it might be better to aim to make it comfortable for all users by putting only the most universally used options right in your face and having the rest easily accessible under a hamburger menu.