db: add pinned column to shows table

bump database version to 2.
make sure old databases are upgraded correctly.
ui: add action bar button to toggle if a show is pinned

currently uses a star icon as they are provided in the action bar
icon pack. would prefer in the future to use something like the pin
icons in the google play music app.
ui: sort pinned shows above others

fixes #7. would still be better to have a pin icon instead of star,
and to display the list of episodes in "pinned" and "others" categories
replace menu icons with ones from android asset studio

removes ldpi, not needed any more. adds xxhdpi.
these are the correct colours for dark action bar, the old ones weren't
change add show menu item labels