Migrate to new file format

[dantrevino]

While the new format is more robust, it will only help loading performance for users with many large notes. Users with many small notes gain some robustness, but will not see any loading performance increase.

Files

riotnotes.json <-- original file
migrated.json

{
status: true,
date: datetime,
log: uri,
backup: uri
} 

index.json

{
 id: xxx-yyy-zzz
 preview: note.text.slice(120),
 img: note.attachments[0],
 fave: note.fave,
 trash: note.trash,
 color: note.color
 tags: note.tags
 modified: note.modified
}

notes/xxx-yyy-zzz.json <--- continue to use the existing note json format
migration-errors.json

{ 
 id: xxx-yyy-zzz
error: error msg
}

tasks

• implement migration & create new files

1. backup to backups/YYYYMMDD-riotnotes.json
2. read & parse riotnotes.json
3. For each note:
   -- create notes/xxx-yyy-zzz.json
   -- append xxx-yyy-zzz to index.json

• update existing actions
  addNote()
• add notes/xxx-yyy-zzz.json
• add to index.json

updateNote()

• update notes/xxx-yyy-zzz.json
• if preview text has changed, update index.json

fetchData()

• if index.json exists follow new loading format
  -- load previews from index.json
  -- on note load/edit, load full note from notes/xxx-yyy-zzz.json

• else do migration

• create new actions
  getNoteById()
  // used when note is opened in the editor

• getFile('notes/xxx-yyy-zzz.json')

• parse note

deleteNoteById()
// used when 'delete permanently' option is used

• delete notes/xxx-yyy-zzz.json
• remove xxx-yyy-zzz from index.json