Server should check for conflicting esbonio installations

[alcarney]

Expected behavior

Especially during the initial 1.0 migration, it's likely people will be trying to use an environment that has an old 0.x install of esbonio hanging around. The server should check for this and advise people remove it.

If at all possible, find a way to work around any conflicts so this can be just an advisory and not a fatal error.

Actual behavior

The existing installation appears to conflict with the injected version and prevents it from working.

See: #778 (comment)

Log output

No response

(Optional) Settings from conf.py

No response