Think about adding/fixing up labnotebook entries on NWB export

[t-b]

We recently had the request to add some more epoch info for TTL channels, see #855.
Now even if we add that now, already acquired data can currently not benefit from this new feature.

We could make this work with the following ideas:

• Never change the labnotebook which was acquired. Only the exported one is touched.
• We never overwrite data only add new entries after.
• Add a new LBN column which denotes that this entry was generated during export. Write that also for normal LBN writing to distinguish.
• Come up with a failsafe approach to add LBN entries to all acquired sweeps. Properly ignore sweep rollback sweeps. We might want to limit the supported labnotebook versions for that.
• Add new entry or fixup existing ones.

[timjarsky]

• support epoch info for old files
  • support short names

[timjarsky]

Modification of original proposal:

• Work on existing NWB files
• Load labnotebooks from them
• Add epoch info for all sweeps
• Write labnotebooks back
• Save NWB file
• Add button to analysis browser, below resave, to overwrite NWB file with retrofitted labnotebook data, respect overwrite checkbox, redesign GUI a bit for that

We need to support files with sweep rollback.

Look into #1147 first.

[timjarsky]

Needs to be completed to enable updating of Institute NWB files acquired before epochs were implemented.