Add 'show_build_panel' Function

- Add function to ask user which file/folder to target when
  building tags
- Fix issue where parent directory was used when requesting build
  in a given directory (due to errant use of 'os.path.dirname')
Add Case For When 'recursive' Flag Set

This prevents the illusion that tags are only being built for the
open file despite the recursive flag being specified.
Add Open Folders to Build Target Menu

- Add all the open folders as targets for ctags scanning
- Fix issue with warning message not being shown when no file or
  folder open
Add Formatting To Folder Dump in Dialog Box
Merge pull request #166 from stephenfin/bug/#94

Resolve issue #94 and issue #164