Function padChannel

padChannel(channel: number): string
Formats a LabJack channel number as the chNN token used in subjects.
Parameters
- channel: number
  LabJack channel number.
Returns string
ch followed by the number zero-padded to at least two digits.
Example
```
padChannel(3);   // "ch03"
padChannel(120); // "ch120"
```
- Defined in subjects.ts:129