Add assets download status to status bar.
Fix "no windows means MMC exits prematurely" issue
S3 bucket listing support and network code refactors.

* Adds support for listing all objects in an S3 bucket.
* Renames a bunch of network related classes (Download->Action)
* Net actions now have static constructors
Fix problem with instance list not using the instance folder path
Valgrind-checked early application start
BLIND CODE, BLIND CODE HERE! WHERE IS THE COMPILER!?!?!

It choked on missing headers, maybe?
Add selectable message box helper, use it, make login GUI error label selectable
Don't make LabeledToolButton selectable
Move "Forget" button to a sane place
Make ConsoleWindow have Qt::Window flag (adds minimise/maximise buttons to titlebar)
Customizable folder browsing is same as for the instance folder. Syste Proxy usage.
Merge branch 'develop' of github.com:MultiMC/MultiMC5 into develop
Hack for Intel graphics drivers on Windows.
List available proxies on start
Revamp Linux build instructions for Qt Creator
Merge remote-tracking branch 'upstream/develop' into develop-nonpremium