conference: use a single counter for CCCP request IDs

[MS-CONFPRO] 2.2.2 says requestId must be a non-negative integer unique
among all requests from the sender. Thus, it's enough, and likely even
more correct, for sipe_core_private to have a single cccp_request_id
counter instead of a separate copy in each sip_session.
conference: refactor CCCP request creation

Moved repeating parts of the code into cccp_request().
conference: use cccp_request() in sipe_conf_add()
conference: use cccp_request() in sipe_conf_create()
conference: use cccp_request() in sipe_conf_modify_user_role()
conference: use cccp_request() in sipe_core_chat_modify_lock()
conference: use cccp_request() in sipe_conf_delete_user()
conference: obtain a list of enabled MCU types

Multipoint control unit types represent conferencing capabilities
enabled on the server (text chat, audio, video, etc.).
conference: refactor CCCP request creation II

Also sip_transport_* requests can be moved to cccp_request(), resulting
in further reduction of duplicate code.
conference: use only supported MCUs in addConference

When creating a conference, allocate only those MCU-types that we know
are supported by the server, i.e. received in a response to our
'getConferencingCapabilities' request.

This fixes 'mcuTypeNotAvailable' error responses when Sipe wanted to use
audio-video conferencing on a server where the option was disabled.
media: notification when conference calls not supported
OBS: sync with latest versions
core: fix stack waste & runtime ineffiencies

Add static storage qualifier to prevent constants from getting copied to
the stack every time a function is called.
Fix #240: Corrupted HTTP response crashes SIPE

A HTTP response with a body but without Content-Length header caused
SIPE to parse the body contents as next HTTP response. This somehow led
to a crash.

sipmsg.c will now set a special error response code instead of just
complaining about the corrupted message. The caller can now decide on
the correct course of action.

As this removed SIPE_DEBUG_LEVEL_FATAL usage from sipmsg.c and therefore
the only usage of this level, it has now been completely removed from
the core and backend code.

Also made sure that the SIP & HTTP input routines abort parsing the
buffer once the connection has been closed.
Fix #241: Adium filters ":" from "sip:"

The string generated in allowedCharacters method obviously was copy &
pasted from another plugin without adapting it to SIPE requirements.
Updated the string to be in sync with sipe-utils.c:escape_uri_part().
l10n: sync translations with transifex.net (hi, te)

- add new language: te
OBS: updates for Ubuntu 14.04
media: update SipeNetworkProtocol enum
media: support TLS relay
media: factor out common stream initialization