New Functionality - addAdditionalSelects()

[lrljoe]

This adds a new method "addAdditionalSelects()" bolstering the "setAdditionalSelects()" method.

When using setAdditionalSelects(), it will always over-write/override the existing additional fields selected.

addAdditionalSelects() will instead append the fields to the "additionalSelects", allowing you to use more code re-use in your tables, using the lifecycle hooks provided. (e.g. the configured() lifecycle hook)

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (4dd0716) 88.51% compared to head (48b2eed) 88.53%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #1609 +/- ## ============================================= + Coverage 88.51% 88.53% +0.01% - Complexity 1344 1346 +2 ============================================= Files 106 106 Lines 3162 3167 +5 ============================================= + Hits 2799 2804 +5 Misses 363 363 ```

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