Add ability to replace local install help forum url

Show the language specific installation help forum url.
marketplace updates
more work on marketplace
more work on marketplace
tweak
Merge branch 'develop' into feature-new-marketplace
updates
continuing work on new marketplace
t strings
making import and export work
merge develop
more work on new marketplace
making marketplace theme and add-on listing pages work
marketplace work
more work on theme detail page, screenshots, slideshow
more work on theme landing page
Fix #1258
styles
Add oauth 1a and 2 generic authentication types, implement a twitter authentication type using the oauth1a controller
C5_execute