Implement soft caching with dexie

[s-blu]

• Cache paragraph notes/labels as well as label value notes
• Dont cache documents for now
• Validate cache entry by generating a checksum via https://docs.python.org/3/library/os.html#os.stat_result , see https://stackoverflow.com/questions/237079/how-to-get-file-creation-modification-date-times-in-python
• Instead of a checksum a concatination of lastmodified/size could be enough, too
• Save those things via dexie into a new database
• Adjust service calls to first check if (a) a cache entry is available (b) if so, if the checksum is OK - if true, deliever from cache

Would be maybe worthwhile to check how more performant that is and if its worthwhlie at all

[s-blu]

Not sure if it makes sense for documents itself, but it could be quite useful for [label] notes

[s-blu]

Maybe the local storage is the complete wrong place here. Storing it in the services, as a map, could be helpful. Especially notes and labels get read all the time, putting unnecessary load on the disk and on writerey