Improve static password format validation

[mickael9]

• Don't reject upper-case scan codes
• Allow 76 characters in the scan code field (was limited to 72)
• Limit the static text field to 38 characters, taking escape sequences into account
• Enforce the 38 characters limit when adding newlines with the Return key

[klali]

Thanks! Merging this with the warning that there's no current plans for making a release of this project.

the merge commit for this was b274cf4c88cd62668c8102effeb411d090c2acad