Implement merging of codeplugs

[hmatuschek]

This is needed to implement the import of CHIRP CSV files. The simple CHRIP format does not contain a proper codeplug for FM capable DMR radios. Consequently, the CHIRP FM channels must be imported into an existing codeplug. Hence, an import/merge function is needed anyway.

This, however, is highly non-trivial, as the elements of codeplugs are linked. So, I cannot simply copy channels, zones, etc from another codeplug. Also, how to handle duplicates? My suggestion would be: Allow the user to select a merge strategy for items (atomic element like channel, contact) and sets (groups/lists of elements like zones, group lists, ...). I.e.,

1. Items: ignore/override/duplicate
2. Sets: ignore/override/duplicate/merge

• Ignore: Duplicate (same name) elements are not imported.
• override: Duplicate elements are overriden.
• duplicate: Duplicate elements are added to the codeplug with modified name.
• merge: Duplicate sets are merged.