[EPIC] New "Manage accounts" view

[JuancaG05]

We want to make several changes and improvements in the current Manage accounts view, so they will be collected in this epic to track the progress. The related issues are:

• [x] https://github.com/owncloud/android/issues/4227: checking and understanding how cookies are handled in the app, so that it is not an impediment removing the key icon in the Manage accounts view for both accounts with Basic or Bearer authentication
• [x] https://github.com/owncloud/android/issues/4301: doing an discovery of the whole account automatically when we login, so that we can remove the sync icon in the Manage accounts view
• [x] https://github.com/owncloud/android/issues/4148: removing the sync icon and the key icon safely after the previous issues are completed, fix a glitch for long usernames and unify the behaviour of the app when the cookies/tokens are invalid in Basic and Bearer auth accounts
• [x] https://github.com/owncloud/android/issues/4312: great improvement in the UI of this view
• [x] https://github.com/owncloud/android/issues/4174: a new icon to clean manually the local storage of the account will be added to the Manage accounts view
• [x] https://github.com/owncloud/android/issues/4175: to complement the previous issue, an automatic cleaning will be provided as well from settings
• [x] https://github.com/owncloud/android/issues/4309: once both ways of cleaning the app are developed, researching about why the Clear data option from the device settings is not working, and if possible remove this option since we'll already have an option to remove local storage manually
• [x] https://github.com/owncloud/android/issues/4335: problem with the temporary folder, containing uploads that, at least, failed once.

[jesmrec]

Everything done!!