Fix #834 - Https connection by default vulnerable to man in the middle attack
Switching from HttpClient to HttpUrlConnection
Redesign of connection configuration screen

- Client authentication tickbox and server certificate are not needed any more
- More space for URL by moving from table layout to relative layout
- Switching client certificate path to an edit field thereby making it possible to remove the certificate
- Switching the select certificate button to a ImageButton
#834 code style
Merge branch 'mamohr-issue-834'