Added the 'Carrier Code' field to the MCC/MNC table. The new field is
supposed to be a constant Multitech-specific indentifier that is constant
between the firmware versions and does not necessarily depends on a
carrier name.

In particular the new field is needed to detect when there is an AT&T
SIM card inserted and 'UE mode of operation' shall be set to CS/PS mode 2.

Restored the original table of MCC/MNC values that was used to populate
the `MTS_IO_MccMncTable.cpp` file.

This step is required to extend the format of MCC/MNC table with
additional fields and re-generate the file based on new data instead of
changing all the lines by hand.

Also added a script that restores the MCC/MNC table from a CPP file.

Extended `create-mcc-mnc-table.py` to support writing the resulting
CPP code directly to the target file:

- refactoring: renamed `print_cpp_mcc_mnc_table` to `print_cpp_mcc_mnc_create_table`
  to better represent its purpose - printing the body of `MccMncTable::createTable()`;
- refactoring: grouped all the `print_cpp_*` functions to the single `print_cpp` function;
- new feature: printing the code directly to the target file without using stdout;
  printing to stdout is used by default for compatibility reasons.

Extended `create-mcc-mnc-table.py` for CSV support:

- refactoring: renamed the 'network' variable to 'carrier' as it's
  named 'carrier' in the CPP code;
- new feature: added support of command-line arguments to select
  the source between the website and CSV; the website is used by
  default for compatibility reasons.

Refactored the `create-mcc-mnc-table.py` script to support generating
`MTS_IO_MccMncTable.cpp` from the website and (in the future) csv files.

The previous script contained a lot of logic related to generating the
MCC/MNC tables in C++ code:

1) printing constant data - functions, comments, etc;
2) formatting and printing the lines with MCC/MNC data;
3) converting MCC and MNC values to unique integers (hashes);
4) parsing the data from the website.

The updated implementation of the script have separated step 4 from all
the other steps which allows to extend the MCC/MNC building logic with
loading MCC/MNC values from a `csv` file in the future.

The behaviour of the script is NOT changed during refactoring. Both the
old and the new version of the script generate exactly the same code
when started on the same source data (website).

Ported the "generate_mcc_mnc_cpp.py" script to Python 3.

Python 2 is not supported anymore and is not included to the modern
distributions of Linux. The transformation is made mainly by `2to3`
without refactoring and with only minimal changes required to support
Python 3.

Fixed carrier MCC/MNC table lookup for networks with two-digit conuntry codes.

The original MCC/MNC population script used the following encoding for MCC/MNC values:

- MCC - interpret the original value as hex;
- 2-digit MNC - append "f" and interpret the resulting value as hex;
- 3-digit MNC - interpret the original value as hex.

So during lookup the system shall also use this conversion logic before querying
the information from the table.