Dropdown for account switching
Use player face in accounts dropdown, grab all valid account skins on startup
Merge remote-tracking branch 'upstream/feature_yggdrasil' into develop
Add support for "no default account"
Could reach end of rulesFromJsonV4 method without returning a QList

It was possible for execution to reach the end of the rulesFromJsonV4
method without returning. This was causing a crash on OS X when parsing
rules inside an instance.
Merge https://github.com/Drayshak/MultiMC5 into develop
Merge https://github.com/brainiac744/MultiMC5 into develop
Merge branch 'develop' of https://github.com/Drayshak/MultiMC5 into feature_yggdrasil
Merge branch 'develop' of github.com:MultiMC/MultiMC5 into feature_yggdrasil
Add icon for when no default account is selected

Also fixed a bug where the icon on the accounts button wouldn't change
when the user checked the "Use as default" checkbox in the account
selection dialog.
Tweak the layout of the accounts button
Verify access tokens before launching Minecraft

Kind of an important thing to do... Heh...