New PJSUA-LIB account option to add user defined parameters to the Contact header

[bennylp]

The pjsua_acc_config.contact_params setting was used to add user defined parameters to the Contact URI. Some applications may need to add user defined parameters to the Contact header, and this will be supported by this ticket.

For consistency with RFC 3261, this will modify the semantic of the existing pjsua_acc_config.contact_params field as follows:

• pjsua_acc_config.contact_params is now used to specify additional Contact header parameters
• a new field, pjsua_acc_config.contact_uri_params, will be added, and this will be used to specify additional Contact URI parameters (the previous semantic of pjsua_acc_config.contact_params)

[nanang]

In r2852:

• Changed semantic of pjsua_acc_config.contact_params, it is now used for specifying Contact header parameters (it was used for specifying Contact URI parameters).
• Added a new field pjsua_acc_config.contact_uri_params, for specifying Contact URI parameters.
• Added fields pjsua_acc_config.contact_params and pjsua_acc_config.contact_uri_params into python pjsua.
• Updated/added option in pjsua app to specify Contact header parameters and Contact URI parameters.

[nanang]

In r2855:

• Updated semantic of contact param in functions pjsip_dlg_create_uac(), pjsip_dlg_create_uas(), pjsip_endpt_create_request() and also variable pjsua_acc.contact to be Contact header value (was Contact URI).
• Updated docs related to above modifications.
• Fixed pjsua_im_send() in generating contact header, it should use pjsua_acc.contact instead, if it is set.

[nanang]

In r2860:

• Fixed compile error for C++ (missing explicit casting from void*).

[bennylp]

In r2883:

• Fixed test failure in pjsip_test, due to Contact URI is now interpreted as Contact header