NIFI-5066: Allow global enable/disable component requests

[mcgilman]

NIFI-5066:

• Allowing the enable/disable buttons to be active under the same conditions as the start/stop buttons.

[andrewmlim]

Changes look good. Enable/disable and start/stop buttons behave consistently. This is minor, but it would be nice if all of these buttons were greyed out (or unavailable in the context menu) when there were no components available i.e. when the process group is empty.

[scottyaslan]

+1 for the UI code.

[mcgilman]

@andrewmlim When no components are selected both enable/disable and start/stop should be allowed as the request will be applied to all eligible components in the current process group.

[markap14]

@mcgilman many thanks for adding this improvement. Code looks good. Was able to verify functionality and everything worked exactly as I expected. +1 merged to master.