fix: disable save button upon submitting #33

Job	Run time
Core Basic - Plone 5 (18.x)	9m 21s
Core Basic (18.x)	7m 21s
Core Basic (20.x)	6m 59s
Core Blocks (18.x)	7m 58s
Core Blocks - Listing (18.x)	6m 50s
Core Blocks (20.x)	7m 31s
Core Blocks - Listing (20.x)	6m 15s
Core Content (18.x)	3m 34s
Core Control Panels (18.x)	5m 7s
Core Content (20.x)	4m 14s
Core Control Panels (20.x)	4m 38s
Coresandbox (18.x)	5m 54s
Core Volto Slate (18.x)	7m 32s
Core Volto Slate (20.x)	7m 28s
Project Generator (18.x)	5m 30s
Project Generator (20.x)	5m 22s
Guillotina (18.x)	56s
Multilingual (18.x)	4m 7s
Multilingual in Seamless Mode (18.x)	53s
Seamless Mode (18.x)	47s
Working Copy (18.x)	3m 17s
	1h 51m 34s

Provide feedback