New feature: Allow use of Pushover priorities.

[CerebralXor]

Also, set default Pushover alert sound to whatever is configured on the receiving device, and fixed bug where unsuccessful notification were not being detected.

• PR is based on the DEVELOP branch
• Don't send big changes all at once. Split up big PRs into multiple smaller PRs that are easier to manage and review
• Read the contribution guide

Also, the current Develop branch has an issue on the notifications page, spitting out a bunch of JS errors which are preventing the Enable toggle switches from displaying the relevant fields (this has occurred after #4913 was merged):

[Vue warn]: Error in callback for watcher "localValue": "TypeError: undefined is not an object (evaluating 'vm._events')"

found in

---> <ConfigTextbox> at src/components/helpers/config-textbox.vue
       <Root>

[ghost]

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[p0psicles]

Sorry for the errors. Is fixed here.. Should be merged today
#5557

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[CerebralXor]

No problems. I'll test this out now that #5557 has been merged and confirm shortly that this PR is tested and ready.

[CerebralXor]

Looks good. This is ready to go.

[p0psicles]

You need to run yarn dev in the slim folder

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