fix(pagination): better protect against invalid inputs

[maxokorokov]

Second attempt to improve situation with pagination invalid inputs (related to #898)

• Added tests for edge cases for collectionSize, page, maxSize and pageSize to see the pagination behaviour
• Cleaned up ngOnChanges
• Essentially the main change is:

if (!isNumber(this.pageCount)) {
  this.pageCount = 0;
}

[pkozlowski-opensource]

@maxokorokov does it fix #898 ?

[maxokorokov]

@pkozlowski-opensource yes it should fix it, as we won't emit NaN

Oops, forgot to add the test that checks that 'pageChange' is not emitted for incorrect values when splitting previous pull request. Amended.