Refactor asserts in api and common packages

lp:~trb143/openlp/asserts (revision 2809)
https://ci.openlp.io/job/Branch-01-Pull/2354/                          [SUCCESS]
https://ci.openlp.io/job/Branch-02-Functional-Tests/2255/              [SUCCESS]
https://ci.openlp.io/job/Branch-03-Interface-Tests/2120/               [SUCCESS]
https://ci.openlp.io/job/Branch-04a-Code_Analysis/1446/                [SUCCESS]
https://ci.openlp.io/job/Branch-04b-Test_Coverage/1263/                [SUCCESS]
https...