Changes after a code review.

Changes after a code review

Adding an ability to set UE mode of operation to libmts-io.

There was added two clear virtual methods in iCellularRadio,
correct implementation for them for Telit LTE modems and implementation
with error messages for all other.

This commit contains the following changes:

- mark all GSM modes as 2G (EGPRS/EDGE is also 2G/GSM);
- mark NB-IoT and CAT M1 as 4G/LTE.

Those changes allow to correctly display 4G modes for MNG2 and 2G modes for all radios.

Small improvements in code comments.

Switched from `sendCommand` with empty command argument to `waitResponse` for URC analysis.

Sending empty string to the serial interface is undefined behaviour according to the POSIX
standart. More of it, we don't need to execute `write` on file descriptor to wait for URC messages.
It was more like a hack than something that was actually required.

This commit removes the hack and replaces it with a proper waiting for a response.

This commit fixes additional issue discrovered after implementation of ACK mode.

When a single 1024 bytes long chunk of data is sent to the radio - the radio reports
that it received nothing. Which is a lie according to Wireshark USB logs, data is
actually sent over USB and looks like radio acknowledged it in USB packet.

This issue is reproducible when chunk size is set to 1024 or 512 bytes. This issue
is not reproducible with chunk size of 256 bytes.

When 1025 or 2048 bytes are sent to the radio - all bytes are received just fine and
we get an ACK string for each 1024 bytes of data.

This commit allows to send 2048 bytes long chunks of data, wait for two ACK strings
from the radio and finish transmission successfully.

During testing I discrovered that EG25-G radio may lose some data during transmission
over Serial AT interface or just freezes and stops responding over Serial AT interface.

When ACK mode is not used, the radio may either return an error:

```
Expected: [+QFUPL: 24312545,fa6b], Actual: [+QFUPL: 17124608,b907

+CME ERROR: 409  // Fail to write the file
]
```

Or it may just freeze on modem_at1 interface and stop responding to AT commands:

```
8:0:34:32|TRACE|RADIO| Sending command [AT]
8:0:34:133|DEBUG|RESULT:

8:0:34:133|DEBUG|Shutting Down
```

This commit implements an alternative, ACK mode for data transmission to prevent data losses.
Data is sent in chunks and the device waits for ACK string from the radio for each chunk.

Added waitResponse overloads to the public interface of ICellularRadio.