[WIP] Check keypad codes + unicode check for user/password

[iranl]

Description:

Related issue (if applicable): fixes #483, fixes #487

Note: Keypad codes checking not tested yet

To-Do

• [ ] Test
• [ ] README update (toggle in webcfg, mqtt topics, keypad section)

Checklist:

• [x] The pull request is done against the latest master branch
• [x] Only relevant files were touched
• [x] Only one feature/fix was added per PR and the code change compiles without warnings
• [x] The code change is tested and works
• [x] I accept the CLA.