doc: Add ModemTechnologies property

This new property in org.ofono.RadioSettings interface will hold the
possible values for radio access technology for the modem.
include: Add method to list RATs to radio-settings
src: Implement RAT list property
rilmodem: Implement RAT list query
mtkmodem: Add parser for 3g capabilities reply

Add parser for the reply to a MTK request that queries the 3G
capabilities of the modem.
build: Compile mtkreply.c
unit: Test 3g capability reply parser
gril: Add slot member

This member is needed by parcel parsers in some cases.
mtkmodem: Add RAT list query
ril: Change atom order creation

This change is needed so RadioSettings interface appears also when there
is no SIM, so FastDormancy and other properties are available when
online.
mtk: Change atom order creation

This change is needed so RadioSettings interface appears also when there
is no SIM, so FastDormancy and other properties are available when
online. Additionally, SIM slot is set in gril object.
test: Add ModemTechnologies to list-modems
Merge pull request #103 from alfonsosanchezbeato/avail-rat-list

List valid modem technologies in RadioSettings interface