Multi-select: implement "select-all" feature and make search bar removable

[tishoyanchev]

Implement a select-all feature for the multi-select component.
Pic related:

The feature is to be enabled/disabled via a Prop called show-select-all with a default value of true.
In additional, make the search-bar also removable via a Prop called show-search with a default value of true.

Note:
If the number of selectable-items is less than the total number of options, the Maximum selectable items is to be ignored when select-all option is clicked.