unify units

* SHARC version:
* Python version:
* Operating System:

### Description
In SHARC different units are employed throughout the code, e.g., mW/W, Hz/MHz, dB/dBm, %/ratio. This may be confusing and SI units should be used always.

### What I Did

```
Paste the command(s) you ran and the output.
If there was a crash, please include the traceback here.
```
