Add rest of cscope lookup modes to commands

 Cleaned up command descriptions to be a little more clear. Added ability to search for remaining useful Cscope search types (4, 6, 7, 8). Moved search mode map to global scope so both worker and UI code can use it. Changed CscopeVisiter to handle navigating via a filename line (required for cscope mode 7 but useful for all modes).

I've tested this with all Cscope modes and verified that the functionality is correct and also that the input panel strings matched the output panel strings and also fit the SublimeText command palette strings.

@ameyp Could you look at this when you get a chance please? =:)