Adapt the blog categories panel to the multi-blog feature

This task is part of the blog application improvement proposal: http://design.xwiki.org/xwiki/bin/view/Proposal/BlogImprovemultiblogsupport

The behavior of the categories panel will change depending on the context where the panel is displayed. For each context we define the behavior as follows:

• aBlog.aPost or aBlog.WebHome
  • List all categories in the category space used by aBlog
  • Manage categories in the category space used by aBlog, use a sheet its WebHome
  • "All" link to the acategory space used by aBlog WebHome
  • categories links to the category page (in its space obviously)
  • counts are the counts matching the list shown on links target

• aCategorySpace.aCategory
  • List all categories in the aCategorySpace space
  • Manage categories in the aCategorySpace space, use a sheet on aCategorySpace.WebHome
  • "All" link to aCategorySpace.WebHome
  • categories links to aCategorySpace.theCategory
  • counts are the counts matching the list shown on links target

• aCategorySpace.WebHome
  • List all categories in the aCategorySpace space
  • Manage categories in the aCategorySpace space, use a sheet on aCategorySpace.WebHome
  • "All" link to aCategorySpace.WebHome
  • categories links to aCategorySpace.theCategory
  • counts are the counts matching the list shown on links target

• Blog.aPost or Blog.WebHome
  • List all categories from the Blog space
  • Manage categories in the Blog space, use a sheet on Blog.WebHome
  • "All" link to Blog.WebHome
  • categories link to Blog.theCategory
  • counts are the counts matching the list shown on link target