Fix issue templates

[hmellor]

The tagging of newly created issues wasn't working and this PR partially fixes it.

Issues:

• Putting [Type]: at the start of the title is unnecessary because, if the labelling is done correctly, it'll be at the end anyway, like this:
  
• Some of the labels specified in the templates don't exist, so they can't be applied to the newly created issues

Solutions:

• Remove [Type]: from templates
• Change doc -> documentation, which does exist
• Change feature -> enhancement, which does exist

Some aspects cannot be fixed with a PR and need to be done by someone with write access to the repo (documentation for this):

• Remove the label Installation and replace it with a label installation
• Remove the label feature request and adopt the default enhancement label
• Create the usage label
• Create the misc label
• Take the opportunity to delete some old/unused labels to reduce clutter (there are currently 34 in total but we only have 8 types of issue)

[youkaichao]

@hmellor Thanks for your contribution!

W.r.t. the title, we would like to keep them. Sometimes we get notifications from email, and the title makes it clear.

W.r.t. the label, I created new labels, and would be happy to accept the following changes:

• Change doc -> documentation, which does exist
• Change feature -> feature request, which does exist

Can you update your PR to meet the above requirements?

[youkaichao]

LGTM, thanks!