This reverts commit 5f5699c5.

Tests failed because they did not allow a charset parameter in
Content-Type headers.

Free text validation is no longer done for abstentions.

This fixes a regression introduced in
9fc360d6.

Real-time updates for global statistics are unnecessary and put a lot of
pressure on the database. Data is now cached for five minutes. The count
of online users is still updated in real-time.

This simplifies analysis of monitoring data.

Configuration for Socket.IO has been refactored to support proxies and
replace ambiguous property names:
* Added API property `socketioPath` to `/configuration/`
* Added property `socketio.proxy-path`
* Removed property `security.ssl`
* Renamed properties:
  * `socketio.ip` -> `socketio.bind-address`
  * `security.keystore` -> `socketio.ssl.jks-file`
  * `security.storepass` -> `socketio.ssl.jks-password`

The default port to bind to has been changed from 10443 to 8090 since
SSL is not enabled by default. There is enough room (8081-8089) for
additional severs (e.g. `grunt run`) in development environments.