add clear cache settings menu
add CacheManager class
add methods to SettingsManger
use AsyncTask to delete cache
add alertdialog to confirm delete cache
use AsyncTask to calculate cache size
clear cache from database
fix build error
clear cache and temp files
fix runtime exception when creating directory
code cleanup
clear thumb files
calculate cache size more accurate
fix conflict

rebase origin master
update strings
reformat code
set cache size unclickable
toast clear cache result
Merge pull request #199 from Logan676/cache

clear cache