Edit menu docs (and some other additions)

[CrashTestJava]

• Document color picking outside of Aseprite
• Menu Bar page structure
• Edit menu page, closes Document the Edit Menu #63
• Adjustments page
• FX page
• Undo history page, closes Create an Undo History page #60
• Replace color page, closes Create a replace color page #64
• Replace outdated info, closes Replace outdated info #62
• Reference layer page, closes Create a reference layer page #61
• Add Theme & Extensions section to preferences
• Text tool page, closes Create a page for the text tool & insert text #66
• Fix dynamics info
• Add missing page footers (I forgot, oops)

[dacap]

Looks good so far! I've made some minor comments that might improve the docs a little.