Nextcloud support

[tostc]

I've implemented the feature request of Issue #20. You can now backup your world to nextcloud. I've generalize some texts, for example

"An error occurred while uploading to Dropbox"

is now

"An error occurred while uploading to {Placeholder}"

• There is now an enum which contains the cloud type(Dropbox, Nextcloud). This is used for the placeholder
• I've move the Dropbox package to a sub package clouds which contains also a Nextcloud package. - The callback class for Dropbox DropboxActivity is now named CloudActivity and is also used by Nextcloud. It's also in the cloud package.
• Because the Nextcloud library was added I needed to enable multidex support for the app, I hope there are no problems with that.
• Added a login Activity for Nextcloud, there you can set the server address your username and password.
• Because the Nextcloud library doesn't support OAuth2, I never save the password on flash.

Hope I haven't forget anything. The new texts for Nextcloud are translated to german and english.

P.S.: Maybe Owncloud will also work, but this is not tested.

[MarquisLP]

Thanks again for the help! This issue has been sitting in the backlog for quite some time, so I really appreciate you having taken it on.

Just now, I've pushed two changes to your branch:

• I've added android:name="androidx.multidex.MultiDexApplication" to the AppManifest, as stated in the docs. Without this, the app would not build.
• I've edited the "Nextcloud Server Address" label to include an example URL, so that users don't have to guess at the exact format.

Other than that, everything works well; I'm able to get the full upload process to work on my end.

One thing I have noticed, though, is that World folders are uploaded to the user's root folder on Nextcloud. Do you know if it would be possible to group all World folders under a parent "WorldScribe" folder, like what we do for Dropbox?

(This isn't a critical issue, but more of a nice-to-have. I'll still merge the branch even if it isn't possible.)

[tostc]

Yes it's possible to group all worlds to a folder like Dropbox. I've added the group function.

[MarquisLP]

Thanks, works like a charm!