[TECHNICAL] Replace dav4android location

[jesmrec]

Current dependency points to:

api 'com.gitlab.ownclouders:dav4android:oc_support_2.1.5'

it should be replaced for another one located in our own repo:

https://github.com/owncloud/dav4android

TASKS

• Research (if needed)
• Create branch technical/replace_dav4android_location
• Development tasks
  • Replace gitlab.ownclouders by github.owncloud from build.gradle file (ownCloudComLibrary)
  • Implement unit tests (if needed)
• Code review and apply changes requested
• Design test plan
• QA
• Merge branch technical/replace_dav4android_location into master