Fix broken link on README

Edit README documentation

Mostly minor changes in phrasing

Improve links in mobile app documentation

Add the PussTheCat.org instance

Fix language detection error

The root cause was load_installed_languages() of argostranslate
being called at the top of the file instead of inside a function,
this caused the list of installed languages to incorrectly be
returned as an empty list.

suggestions: Abort when missing parameters

app: Fail when giving invalid API keys

- Remove unnecessary import
- Reorder imports
- Fix whitespace issues

When an API key is passed, fail in the case of an invalid API key even
if an API key is not required. This allows the user to know that the API
key is invalid. Otherwise, they work under the assumption that the API
key is correct, even though it is not.

added my instance :)

keep selected languages and text in url

set default language instead of raise error

Add --disable-web-ui

add python 3.9

unescape html entity codes (ex: &apos)

Upgrade to pyicu>=2.8