DatabaseProperties: Implement functions and tests

[tsubotitsch]

• Check if function is nesesary for each property
• Add a test for each function
• Add a test for each property

[fasteiner]

Class Tests: working until tests/Unit/Classes/Database/DatabaseProperties/12_dp_multi_select.Tests.ps1

[fasteiner]

All class tests finished, all property classes fixed.

[fasteiner]

reopened, as this was only a intermediate release and the functions and their tests are still pending implementation