Client-side exception handling

[mbollmann]

Originally reported by: Marcel Bollmann (Bitbucket: mbollmann, GitHub: mbollmann)

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Exceptions in the GUI shouldn't usually occur, hence the name "exception".

However, if anything does go wrong, the GUI just hangs. This is bad[tm] -- if this happens during a loading screen, the user is under the assumption that the loading still continues; if this happens at some other time, some parts of the GUI (or maybe everything) just stop working without any indication why.

At a bare minimum, CorA should:

• Signal that an exception has happened
• Try to save any unsaved changes if a document is currently opened
• Reload the page or instruct the user to do so

Some resources:

• Catching all javascript unhandled exceptions
• How to catch JavaScript Errors with window.onerror

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• Bitbucket: https://bitbucket.org/mbollmann/cora/issue/41

[mbollmann]

Original comment by Marcel Bollmann (Bitbucket: mbollmann, GitHub: mbollmann):

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Handle errcode -2 in server request (re issue #41)

[mbollmann]

Original comment by Marcel Bollmann (Bitbucket: mbollmann, GitHub: mbollmann):

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Handle all JavaScript errors (fix #41)

[mbollmann]

Original comment by Marcel Bollmann (Bitbucket: mbollmann, GitHub: mbollmann):

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handle errcode -2 (uncaught exception)