Added TableViewCol and Checkbox to components property (so that custom versions can be inputted)

[patorjk]

The "components" feature of this table allows for users to override internal components with custom ones. This PR adds the two additional internal components that can be overridden:

• TableViewCol: The popover that allows columns to be hidden/shown. To make it useful, an "updateColumns" callback is now passed to this component making it so features like "select all" can be added. (Unable to show/hide columns with CustomRowRender #1250 (comment))
• Checkbox: The ability to override the checkbox component (for example, if you wanted to set its color or other properties). (Customize color of the select row checkboxes at the side of the table #1255, Rather than checkbox is there a way to make star? #1249)

The custom components example was updated to show these two updates in action.

[coveralls]

Coverage increased (+0.3%) to 71.434% when pulling 03df2b3 on customComponents320 into 2d6c628 on master.