To be compatible with Redmine 2.6 ...

- Updated jquery.jstree (1.0 rc to 3.0.8)
 - remine_re_controller and requirements_controller refactored due to API changes
 - refactored and rewritten JS due to API changes
 - refactored and rewritten jQuery event watchers
 - changed to use ajax call instead of prerended data
 - changed a code in issue creation since parent tree nodes should be expanded
 - uploaded and changed lots of related assets

- Updated jquery.layout (1.3.x to 1.4.3)
 - mostly changes in redmine_re.js asset
 - uploaded and changed lots of related assets

- Other refactorings and changes
 - removed "if logger" statements since they are not needed and were used inconsistently
 - some code cleanups mostly in the files I needed to work on
 - some refactorings in icons css (mostly icons.css and redmine_re.css assets)