New 'u-blox' plugin (v3)

[Aleksander Morgado]

Hey Dan & everyone,

This is the 3rd update on the 'aleksander/ublox' branch, with this
additional changes done after Dan's last review:

 * Recovered the original DENIED registration state logic.
 * Implemented a generic +CFUN parser and then included
plugin-specific parsers for the ublox, linktop and mbm plugins,
including unit tests.
 * Fixed the +UPINCNT patches which had some code squashed in the wrong commit.
 * Fixed RSRQ logic in +CESQ parser.
 * Updated +UBANDSEL parser to use g_strchomp() to get rid of trailing
whitespaces, including CR and LF.

Reviews of the implementation are more than welcome.
https://cgit.freedesktop.org/ModemManager/ModemManager/log/?h=aleksander/ublox

Cheers!

-- 
Aleksander
https://aleksander.es