Show an error message if synchronization fails

[korelstar]

I've tested the app (v0.8.1 from F-Droid on Cyanogen OS 13.0 / Android 6.0.1, German) with some ownCloud servers and it appears, that the app does not show any message, that informs about errors during login or synchronization (except if the server address is wrong).

I.e., no error is presented and it looks like everything is fine for the following cases:

• If I connect to a server with wrong user name and/or password
• If I connect to a server on which the ownCloud Notes app is not activated or even available (i.e. ownCloud 7)
• If I change or create a new note, there is no clue, if this note is synchronized successfully or not

Therefore, I suggest to show meaningful error messages if

• the login fails,
• synchronization is not successful

AND introduce a small icon at the right margin of each note in the ListView (main activity) which is shown if the corresponding note was not synchronized yet (e.g. since it is new or was changed). With this, you have a good overview if everything is fine and it does not bloat the app layout in the normal case (everything is sync'd).

[korelstar]

I just looked at the source, and found out that there should be indeed a Toast, if the login fails. However, the validation depends on the HTTP response code. Unfortunately, this does not work, if the Note app is not installed on the server. Here, the server always responses with status code 200. Hence, the HTTP response code check is not sufficient! You can test it with https://demo.owncloud.org/ which doesn't have the Note app installed, too.