added multiple checkbox support:

* forgot config
* re-added checkbox
* should check for checkboxes not checkbox when adding options.
* removed leftover code (shame on me), added more thorough check for checked.
* took the checkboxes creation outside of config, added usage of labels, also checks for '[]', it should always be appended
* indentation
Cleanup code.

Signed-off-by: crynobone <crynobone@gmail.com>
Remove whitespace.

Signed-off-by: crynobone <crynobone@gmail.com>
Merge branch '2.1' into 2.2

Signed-off-by: crynobone <crynobone@gmail.com>

Conflicts:
	src/Html/HtmlServiceProvider.php
	src/config/form.php