Bugfixes after Release Candidate Review

• allow default obfuscation proxy pinning values in RiseupVPN, disallow them in Bitmask
• set minSDK to 21 since upstream did so, too, closes #9052 (closed), #8934 (closed)
• fixing some memory leaks, hopefully fixes #9122 (closed)
• fix layout issue on phone with low density if vpn runs without network
• fix #9121 (closed)
• fix text colors in buttons in RiseupVPN
• fixing app crash while setting actionbar title
• adapt on-off button icon sizes
• reduce shadow below main on-off btn
• remove gradient from location button
• center and capitalize action bar title (BITMASK)