Low surface brightness issues from tutorial

[kadrlica]

• Fix link to guided tour of calexp (missing link)
• Replace noise replacement with meas.base.NoiseReplacementTask (takes a footprint set)
• In if False change exposure to calexp
• Add credit to Johnny Greco for original notebook idea

[kadrlica]

I've decided to keep the masking procedure the same, but to write another markdown cell about the noice replacer.

[kadrlica]

This was closed by #100