[EPIC] Improvements in accessibility

[JuancaG05]

The app needs several improvements in accessibility terms. We'll group them here to have them all together. The related issues are:

• [x] https://github.com/owncloud/android/issues/4360
• [x] https://github.com/owncloud/android/issues/4361
• [ ] https://github.com/owncloud/android/issues/4362
• [ ] https://github.com/owncloud/android/issues/4363
• [x] https://github.com/owncloud/android/issues/4364
• [ ] https://github.com/owncloud/android/issues/4365
• [ ] https://github.com/owncloud/android/issues/4366
• [ ] https://github.com/owncloud/android/issues/4367
• [ ] https://github.com/owncloud/android/issues/4368
• [ ] https://github.com/owncloud/android/issues/4369
• [ ] https://github.com/owncloud/android/issues/4370
• [ ] https://github.com/owncloud/android/issues/4371
• [x] https://github.com/owncloud/android/issues/4372
• [ ] https://github.com/owncloud/android/issues/4373
• [ ] https://github.com/owncloud/android/issues/4374