Make window UI elements reorderable

[numeredev]

DESCRIPTION

What does your feature request improve on? Please describe. The editor tabs are already moveable around, however, people may actually want to reorder the complete UI to their likings.

Describe the solution you'd like Make all window elements reorder- and repositionable and store their assignments for next start-up as indicated in #764.

Additional context Migrated from here: https://sourceforge.net/p/numere/tickets/766/

(Do not write below this line)

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DEVS' SECTION

ANALYSIS

(Describe, what's the issue and which changes have to be made)

IMPLEMENTATION STEPS

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• Implement the necessary changes in a new branch created here on GitHub
• Test your implementation

DOCUMENTATION STEPS

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• Update the changes log
• Add comments to your implementation
• Add Doxygen documentation comments
• Create or update the documentation articles (*.NHLP and *.NDB files, if needed)
• Update the language strings (*.NLNG files, if needed)

PULL REQUEST

• Create a pull request for your changes
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