New: added 'Clang' tab in the output view with to expose the following:
- shows clang output for various code completion actions (more detailed errors, etc)
- change codelite's caching policy for clang translation units (hereon: TU) (i.e. parse file on-load or when CC is actually required)
- allow the user to clear codelite's clang TU cache and force a reparse of a file