FORUM-717 Cannot hide categories/forums scoping.

Fix description:
* Optimize isShowCategory and isShowForum methods.
* Check category/forum visibility settings in UIForumPortlet class.
FORUM-826 [Quick Creation of Topic/Poll] Only show space when there are forums in intranet and space

Problem analysis:
* Mix the filtering of forums for Quick Creation in case of intranet's forums and those in spaces.

Fix description:
* Remove space's forums from filterForumByName method so that this filter only handles intranet's forums.
  Space's forums are handled later in UICreateForm.
FORUM-892 [IE8] Content of FCKEditor isn't updated after adding attachment for topic, post, question

Problem analysis:
* In this old FCKEditor (2.6.2), the whole content of FCKEditor (which is an iframe) isn't updated when coming back from Attach File (another iframe) in IE8.

Fix description:
* Write submitFCKEditorForm to handle the issue with IE8 browser.
  This method invokes directly FCKEditor's UpdateLinkedField to update FCKEditor's content.
* submitFCKEditorForm is invoked when the user clicks Submit/Preview buttons in Topic/Post/Question form.