Fixes issue #8065: Answer code conversion to '0'

DEV: when exporting to CSV/EXCEL etc. and conversion
DEV: of Y or N to '0' was chosen, values were wrongly
DEV: exported as 'missing values' (empty)
DEV:
DEV: nasty php typing problem....probably same problem
DEV: with issue #8039
small change to also honor 'false'

thanks to Shnoulle
use is_null instead of !isset
Merge pull request #100 from mfaber/zeroconversion

Fixed issue #8065: Answer code conversion to '0'
added json export capability

Now lime survey can be exported in json format also.
Added a simple private method that will convert xml to json.
the survey is first exported into xml using the current available functionality, and then later just translated to json and then output.
dev: fixing add survey for non-superadmin user
dev: Fixing some more permission errors
Fixed issues with touch screen due to not including
jquery-ui-touch-punch.
Fixed issue: #08085: PHP notice at public statistics and miscalculation on quartile
Dev: recordCount are not reset when change field. But needed for NULL value
Merge branch '2.05' of github.com:LimeSurvey/LimeSurvey into 2.05
Merge pull request #115 from rohitmp/2.05

added json export capability
-- Thanks for the contribution!
Update release_notes.txt

Incorrect system requirements (2.05 requires php 5.3)
csrf off