Summary:
Use Storage Access Framework on Android running SDK >= 21 so writing to
sdcard will work again

|{F6546802}|{F6546803}|{F6546804}|
|API 21+|API 19-|Edit|

Test Plan:
Install patch on Android phone with Build.Version < 19 (Kitkat)

- Without a sdcard: Verify that dolphin displays an "All Files" entry that is empty
- With a sdcard and with "Add camera folder shortcut" turned off: Verify that dolphin displays the configured display name of the sdcard
- With a sdcard and with "Add camera folder shortcut" turned on: Verify that dolphin displays the configured display name of the sdcard and also lists a "Camera pictures" shortcut
- With a sdcard: Verify that when changing the display name or the "Add camera folder shortcut" preference dolphin displays the updated items (after pressing F5)
- With a sdcard: Verify that files can be read and written to/from the sdcard

Install patch on Android phone with Build.Version < 19 (Kitkat)
- Repeat the above tests except for the read/write test: Verify that files can be read from the sdcard

Install patch on Android phone with Build.Version > 21 (Lollipop)

- Without any configured storage locations: Verify dolphin displays an "All Files" entry that is empty
- With configured storage locations: Verify dolphin displays the display names of the configured storage locations and that entering a location displays the correct directory entries
- Make one or several changes to the configured storage locations: Verify dolphin displays the display names of the configured storage locations (after pressing F5) and that entering a location displays the correct directory entries

Reviewers: #kde_connect, albertvaka, sredman

Reviewed By: #kde_connect, albertvaka, sredman

Subscribers: albertvaka, sredman, kdeconnect

Tags: #kde_connect

Differential Revision: https://phabricator.kde.org/D18212