Block changing portrait if the user has not unlocked it

[sarimash]

Description

Verification steps:
Inspect a locked portrait, delete 'disabled' from the properties on that ion-avatar

Select newly unlocked avatar and hit confirm
The following error should pop up:

Fixes #9

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have run tests (npm run test) that prove my fix is effective or that my feature works