Iop temperature show enable button

Before #623, temperature iop must always be on because it was used as a conversion point from uint16_t input to float output because it was the first iop that is always enabled.
But even then user could select preset ``passthrough``, which essentially turned iop into:
```
read uint16_t pixel;
convert to float;
multiply by 1.0f (because passthrough);
divide by 65535.0f;
write float pixel
```
After #623 this pseudo code would look following:
```
read float pixel;
multiply by 1.0f (because passthrough);
write float pixel
```
Since x*1.0f == x, we can just skip this iop (out == in).
And since we can skip it, why not let user disable it if he want's to?