[FEATURE] Select multiple files to delete

Integrate checkboxes to delete multiple files.

Add TSconfig option »deleteCheckbox« to switch delete
action from buttons to checkboxes.

Add TSconfig option »deleteAllButton« to show/hide the
action to delete all files at once.
[TASK] Rename options to show/hide buttons
[TASK] Add options to show/hide buttons to documentation
[TASK] Raise version to 0.3.0