code cleanup
Store used zim file persistently; Show (wip) welcome page ; clear history after open(not working)
Add back to action bar; back and forward icons added

http://developer.android.com/downloads/design/Android_Design_Icons_20120814.zip
Note: Renamed. (compile error because names started with number, oddly
first compile (with number in name) worked fine).
Note: ldpi missing. Effect unclear.
Commented Implementation of webviewclient use. (for now stay with default)
Use CursorLoader (API level 11) in zim file selection

Higher responsivness in UI. (because previously used query runs
in main(=ui) thread) However, benefit not that impressive on Galaxy Tab 2
(may however easily have more effect on slower devices)
Fix hangs on article load (progress bar was stopping in middle)

Issue was that in case of errors (i.p. some resources not found) outputstream
was not closed.
format fixed
Check that article available before loading

Allows for error handling, else errors in worker thread just lead to
return of empty data
articleSearchField hint text (Type to search...) added