Convert strings in plugins part 2

- Convert strings in custom
- Convert strings in images
- Convert strings in media
- Convert strings in presentations
- Update projector-pjlink test

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lp:~alisonken1/openlp/strings-plugins2 (revision 2667)
[SUCCESS] https://ci.openlp.io/job/Branch-01-Pull/1571/
[SUCCESS] https://ci.openlp.io/job/Branch-02-Functional-Tests/1482/
[SUCCESS] https://ci.openlp.io/job/Branch-03-Interface-Tests/1420/
[SUCCESS] https://ci.openlp.io/jo...