Add option to rename partitions in partition manager.

[richrd]

Add option to rename partitions
- Sanitize the partition name
- Prevent renaming protected partitions
- Prevent duplicate partition labels

Background:

Some firmware, e.g. retro-go use multiple partitions, so that the main app launches "sub apps" by referencing the partition where the sub app is by name. It's possible to install these partitions individually with Launcher, but for them to work together the partitions need to have the correct names. This feature will enable renaming them to the correct names that the firmware expects. It does not add support for installing firmware with multiple app partitions, so that part is still a manual step.