[a11y] Correct label for each activities and fragments

[Aitorbp]

Is your feature request related to a problem? Please describe.

In relation to this issue #4373, we have noticed that when we have talkback enabled and we are switching between activities/fragments, talkback reads the word ownCloud for each change.
This is not accessible to users, since the word ownCloud does not provide much information to define which view the user is on.

Describe the solution you'd like
A possible solution would be to add the android:label in the AndroidManifest.xml in each activity to the correct name.

In the case of fragments, we must change the label through the setTitle. Example below:
activity?.setTitle("The new label here")
Doc: https://stackoverflow.com/questions/27918701/android-fragment-change-title

TASKS

• Research (if needed)
• Create branch feature/correct_label_for_each_activities_fragments
• Development tasks
  • Added label to activities
  • Added setTitle to fragment
• Code review and apply changes requested
• Design test plan
• QA
• Merge branch feature/correct_label_for_each_activities_fragments