Started work on storing path objects in service file.
Refactored save code and reduced duplication.
Fixed + improved the loading / saving progress bars
improved performance

loading powerpoint from a service still does work

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lp:~phill-ridout/openlp/pathlib12 (revision 2817)
https://ci.openlp.io/job/Branch-01-Pull/2428/                          [WAITING]
[RUNNING]
[SUCCESS]
https://ci.openlp.io/job/Branch-02a-Linu...