Add packages job

This job can be used to install and remove packages.
Merge pull request #116 from plfiorini/packages

Add packages job
Partitions icon.
Automated partitioning icon.
Add icons to qrc.
Added WaitingWidget to libcalamaresui, wrapper for QtWaitingSpinner
Add ClickableLabel, a QLabel which emits the clicked signal.
Add new icons to CalamaresUtilsGui
Make the locale viewmodule use WaitingWidget.
Make the prepare viewmodule use WaitingWidget
New PrettyRadioButton, an alternative to QRadioButton with rich text.
Prefer nullptr over 0.
Add ChoicePage to partition module + OS detection with os-prober.
Expose icon and tooltip in DeviceModel.
Add isDirty check to PartitionCoreModule
Add page for erase+install operation.
Attempt at a window size fix.
Size policy on erase page.
Fix page flow issue in partition module.
Add clearJobs to PCM