Use more generic names for stoken_*

libopenconnect now supports both TOTP and RSA software tokens.  Change
our local naming to align with the new library APIs.

This shouldn't affect functionality, stored user settings, or
configuration import/export.
Allow alphanumeric software token secrets

RSA uses (mostly) purely numeric secrets, but other schemes may have
different requirements.

We will still strip out non-ASCII characters to avoid problems like
linefeeds showing up in the exported VPN configuration files.
Add support for TOTP software tokens

Create new TOTP option on the UI, and make the appropriate library calls
if the user enables it.
Dynamically remove unsupported token_mode entries

Depending on which software token libraries are installed, this could
include stoken options, TOTP options, both, or neither.  Only show the
user the options that are available on his system.
auth-dialog: Introduce FORMCHOICE helper macro

libopenconnect >= 3.0 uses a pointer array so we need to change the way
the "choices" field is accessed.
auth-dialog: Add support for NEWGROUP

When the user selects a different authgroup, return NEWGROUP to
libopenconnect to allow it to refresh the form.  Different groups may
require different prompts.

Also, if secondary_username is provided by the server, prepopulate the
form field.

[dwmw2: Update to use form->authgrop_opt and fix crash due to calling
        gtk_dialog_response() from combo_changed callback.]
auth-dialog: Add support for OC_FORM_OPT_IGNORE

Hide any options that libopenconnect doesn't want us to display.
Run make update-po
Import translations from master