Add compatibility for mobile apps + user profile page

[tobihagemann]

The following changes have been done to add compatibility for Cryptomator's mobile apps:

1. Added type to the Device entity and made sure that DESKTOP is default.
2. Added custom HTTP header to unlock response so that mobile apps can distinguish between free/paid licenses.

But as you can see, there is still this temporary code:

return Response.ok(access.jwe).header("Cryptomator-Mobile-Access", license.isValid() ? "READ_WRITE" : "READ_ONLY").build();

I'm not sure what to name this header and what it should represent yet. E.g., if it's set to READ_ONLY but the user has bought the full version of the app, they should still have read/write access. That could be confusing. A different approach would be to have a header named Hub-License-Edition with COMMUNITY and STANDARD or something like that.

Furthermore, I've copied other useful changes from the feature/refactored-access-grant branch:

• Added user profile page, which combines the device list and user settings. (Fixes #187)
• Considered BROWSER device type already, even though it's not used yet.

[infeo]

For documentation: We talked about the custom header and if it can be faked. An idea is to sign the header with the vault key or the vault owner, in order to ensure that this is not possible.

[tobihagemann]

Update on faking the custom header: It's impossible to sign the subscription state at the moment because this information is only known to the backend. We would need to introduce a new key pair for Hub and this is out of scope for this PR. However, we make sure that the mobile clients have to explictily check for the ACTIVE and INACTIVE values. When we introduce a signed subscription state at some point and use a different value, old mobile clients should treat it as INACTIVE.