[#1] Add "filesystem-path" string format type and accompanying widget.
[#1] Implement custom file browser to support future functionality such as sequence identification.
[#1] Implement simple filesystem model.

Not currently using QFileSystemModel in order to simplify future sequence management.
However, this does mean this model has some inherent performance drawbacks.
[#1] Add fallback icons.
[#1] Add icon for collections.
[#1] Support collections of files in model and refactor to limit use of incompatible QFileInfo interface.
[#1] Support sorting directories before files in Filesystem model.
[#1] Improve sizing of table columns.
[#1] Use new browser in custom filesystem path widget.
[#1] Add Clique to requirements list.
[#1] Remove redundant code now that Clique 1.1.0 is available.
[#1] Hide bookmarks widget for now.
Merge pull request #10 from 4degrees/1_specialised_datum_widget

[#1] Specialised datum widget