Offer backup intervals according to datasource and datasink properties

[WolfgangEibner]

Only offer backup intervals above the higher one of the allowed interval of datasource and datasink. Properties should already exist in REST API.

E.g. Job saving Moodle to Dropbox:
Moodle plugin minimum backup interval: weekly
Dropbox plugin minimum backup interval: daily
UI offers weekly and monthly

[fetzig]

Properties should already exist in REST API.

couldn't find it. and can't remember of seeing it in the past. docu says nothing about that either.

so please add it to the api and api doc, and/or point me to the right direction. thx.

[WolfgangEibner]

Issue from the 5th consortium meeting: If an input and an output plugin differ in their possible backup intervals we can only take the ones which exists in both. As we do not have gaps like daily, yearly we only need the minimum interval for both plugins (input and output) and offer the highest one of them. Not a high priority issue.