Plotting images does not fully respect tolerance and units

[kuwisdelu]

Currently, tolerance and units are only used to process the matched m/z features for creating the image. They are not passed to features() to perform the initial matching, which leads to confusing errors when the feature is not found despite using a larger tolerance.

It should be fine to simply pass tolerance and units to features() -- are there any unforeseen issues this could cause?

In addition, we may need to print more digits on the error and warning messages. Switch to using format()?