Fix sorting and grouping of staging entries by state
- group all states, states which require attention more frequently come
first
- also sort staged changes pane
- alphabetic sorting is the natural order and doesn't need explanation,
hence name the button to toggle sort order "Sort by state" and use a
new icon depicting that
- rename the comparator to StagingEntryComparator since it's now used
for both unstaged and staged changes
Bug: 473919
Change-Id: Ia6c165f252bb293d77251e4b5cf9dfb63c1c5d53
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>