fix some annotations-in-text issues

[peterstadler]

Description, Context and related Issue

There surfaced two issues when testing with the Open-Faust data which might be connected to #460.

1. JSONification of the local:getAnnotations function was not complete. The function returned a map object plist as string, causing some Javascript function to fail.
2. teitext:getLabel#2 would return a sequence of strings (under some circumstances) which was not allowed by the return value of the function signature.

Refs #460

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Improvement
• Refactoring

Overview

• I have performed a self-review of my code, according to the style guide
• I have read the CONTRIBUTING document.
• All new and existing tests passed.

[peterstadler]

For reference: This can be reproduced with the Open-Faust data by clicking on the "Edition -> Text" entry from the navigator and activating the annotations. getAnnotationsInText.xql will return data but in the wrong format (string instead of an object) which causes some Javascript to fail (see Console).

[feuerbart]

looks good to me, annots are returned correctly.