Bring MINDJAIL and HTTPGET support into the main libopm, but with intention to

Bring MINDJAIL and HTTPGET support into the main libopm, but with intention to
break every protocol off later into individual modules.

Remove hard-coded configuration options, now change all config keys to be
strings.

The default config keys required by the provided protocols are added when
opm_create is called, but additional keys as used by any contributed protocols
can be added by the caller using opm_config_add.