Add a custom widget for editing and selecting paths. Implemented in OpenLP, with the exception of the import wizards, as I have other plans for refactoring these!

lp:~phill-ridout/openlp/path_edit (revision 2737)
[SUCCESS] https://ci.openlp.io/job/Branch-01-Pull/2009/
[SUCCESS] https://ci.openlp.io/job/Branch-02-Functional-Tests/1919/
[SUCCESS] https://ci.openlp.io/job/Branch-03-Interface-Tests/1855/
[SUCCESS] https://ci.openlp.io/job/Branch-04a-Code_Analysis/1235/
[SUCCESS] https://ci.openl...