fix: generate-page

[michalsn]

Description
This PR fixes a few issues with the current generate-page script implementation, described below.

I have noticed a two things:

• information about Missing keys that are in a nested array is not displayed
• there is no information about missing files (if there are any), therefore missing files are not considered when calculating the overall translation percentage for the locale

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[MGatner]

The code looks good without going through it too thoroughly. Would you please share a couple before and after pics?

[michalsn]

Sure, here you go.

Before:

After:

[MGatner]

Very nice, thank you @michalsn