Command log to debug reconnects.

The content of this commit should be removed from the final fix.
Special debug log: "OpenVPN log" tag

The log shows all state commands, and notifies when bytecount values have not changed more than 3 times in a row.
Logbuffer copied to Logcat.
No new routes if openvpn is already running.

We cannot add routes to an existing openvpn session because it makes openvpn reconnect.
Merge branch 'bug/vpn-reconnect-sometimes-hangs' into develop
Renamed certificate handling methods.

I still let one method to bypass hostname verifier, otherwise dev.bm
will not work.

I've reduced downloading functions to 3: download without CA, download
with commercial CA and download with provider CA.

I only download CA cert once, when the user selects the corresponding
provider. Each time a user switch provider, the cert is downloaded
(along with other json files).
AlertDialog for failed downloads.

The dialog shows only an "OK" button to dismiss it, and the reason why
the download failed.

Right now, this dialog appears if a download is not successful. If it's
too intrusive, I can remove some cases. Let's try how it feels.
Fixed a typo in the rebase.
Merge branch 'bug/overly-complex-certificate-verification-method' into develop