Added "DATE" form type that works like the "DATETIME" type incl. date picker, just without time details.

This reverts commit 9d3f2bbc.

This reverts commit aab7e05b.

- made placeholders visible for apache, too
- added event raise at formdef loading (on_before_formdef and on_after_formdef)
- added possibility to put plugin files into module/lib/plugin.d/ directory

- Added: First version of client api access with client user credentials
- Changed: 
  - merged remoting_lib and tform into one new base file where appropriate
  - moved some methods into helper methods
  only those methods remain in remoting_lib or tform that are completely
  different in these files or are only used in one of them
- Changed: added check of _GET array in json api handler