take care of directory that we don't have permission
add ant prerequisite for Android build
Merge pull request #621 from chrox/master

take care of directory that we don't have permission
fail gracefully when the Kobo light device cannot be opened
os.execute may cause FC on Android
font weight option should be persistent between launchings
This should fix #620.
update pot file
Merge pull request #625 from hwhw/master

fail gracefully when the Kobo light device cannot be opened
Merge pull request #626 from chrox/master

font weight option should be persistent between launchings
fix(setting): handle empty setting files properly

empty reader setting evalues to nil
Merge pull request #627 from houqp/houqp-master

fix(setting): handle empty setting files properly
adapt reader footer for small screen
adapt touch menu for small screen
strings not shown on GUI will not be translated
This may encourage users in transifex to join Koreader project.
add option to load last opened file automatically
adjust option orders in readermenu
fix license version in reader usage
add previous and next chevron icon in touch menu
add Korean in language table
now make po should be issued manually