Script-Fu Console: Misc fixes and trivial screenshot removals
- Remove confusing screenshot with obfuscated button names. There is nothing secret about button names.
- Rephrase text about procedures and their parameters to be also understandable without having looked at the (removed) example image.
- Remove unneeded screenshot depicting an "Apply" button. This is self-explanatory.
- "Apply" button is not "at the bottom" in GTK 3 under GNOME.
- Do name things. No "this button" or "an additional button".
- Spell "textbox" like in all other docs: "text box".
- Misc typo fixes.