Drawer submenu capability.
MainDrawer submenu implementation.

temp. commit
Make ViewPager update it's fragments of period change.
Fix snap-positions.
BarChart empty and loading states.
Add stability.
BarChart refactor.
Make drawer subitems and parent items highlight correctly.
Focus on last selected period when returning to reports.
fixed reports and pager to integrate with previous content
Merge pull request #413 from toggl/taavirehemagi-reports-monthyear

taavirehemagi-reports-monthyear. Closes #402