Add "hardware lease" capability

To avoid situations where scdaq is controlled by multiple function managers (or scripts, etc.) we could introduce the concept of a hardware lease. It may be useful to, e.g. return a token as a response to a configuration (if #13 is implemented).

Invalidation of the token should only be possible in three ways:

• Release with the use of the token itself (i.e. this should be only possible by the application holding the lease)
• Manual action (e.g. restart SCDAQ, delete a .token file if we store it that way, etc.)
• Possibly: Timeout after, e.g. one minute (the FM has a monitoring interval of 10 seconds, so this should give enough margin to renew the lease)