Custom apps ZIM migration

[BPerlakiH]

Fix for #601 - Migrating bookmarks for custom app.

There were a couple of thing to do:

• make sure we migrate the bookmarks
• migrate the tabs, which have "interactive data" - a kind of snapshot of the tab for webView, in a form of Data, which is now migrating at the point of opening the URL from that data
• make sure we delete the old file reference in the DB - as currently we were displaying a list of local ZIM files in the menu, (up to 5). For custom apps it should really be only 1 item, so we make sure we remove the reference to the old ZIM file.

[kelson42]

@BPerlakiH Can you please fix the codefactor?

[kelson42]

@BPerlakiH Ready to review?

[BPerlakiH]

There's one more thing need to be fixed here, which is the "interactive data" saved together with the state of each tab.
Will update the PR soon.

[BPerlakiH]

@kelson42 @rgaudin it is ready for review.

[rgaudin]

Can't say much