Clean up QML/JavaScript, EntryComment: Refactor code and layout

Implementation-wise this is better than the status-quo, however UI still needs a bit of polishing.

Resolves this warning:

kf.i18n: 0 instead of 1 arguments to message {%1 <i>(author)</i>} supplied before conversion.

For the review text, swaps QQC2.Label with Kirigami.SelectableLabel and explicitly specifies its format as TextEdit.RichText.

Manual icon management was replaced with Kirigami.Avatar type.