Import for GoogleKeep and Evernote

[PhilKes]

Closes #53

• Adds the possibility to import from Evernote and Google Keep

notallyx_importers_googlekeep_evernote.webm

• For each Importer there is a help dialog with a link to the official documentation, since you need to export from the specified app first

Evernote

• Export of a Notebook as ENEX can be imported
• Imports Notes, Tags, Files/Images/Audios (decoded from base64), Tasks/List Items
• Text formatting is also imported (bold, italic, monospace, strikethrough, links)
• Evernote does not have archived notes, and deleted Notes are not exported, therefore they cant be imported either
• Evernote does not export which notes are pinned, therefore this information cant be imported

Google Keep

• Google Takeout ZIP can be imported (uses only json files + attached files from ZIP)
• Imports Notes, Tags, Files/Images/Audios, Tasks/List Items
• Text formatting is also imported (bold, italic, links), Google Keep does not offer monospace or strikethrough formatting

Audio recording durations

GoogleKeep exports the audio recordings as .3gp, Evernote as webm, the audio files itself are correctly imported and can be played, but their duration metadata seems to get lost, therefore NotallyX cant know how long they run. I will further investigate this, but in the worst case the user will just not be able to see how long it is, which is not that bad.

Note Colors

Even though Google Keep and Evernote allow to color notes, they are currently not imported since NotallyX only has a predefined set of colors.

Other App Importers

In the future I will maybe add more importers for e.g. Microsoft OneNote, but I dont want to implement it for every other Notes app out there, so if you have a specific app you need an importer for, feel free to open an issue