Add feed id to subscribe to feed response

As described on the forum, this proposed change is to make the subscribeToFeed API response include the feed_id of the new or existing feed.

https://tt-rss.org/forum/viewtopic.php?f=8&t=3893

Thank you.

John

See merge request !35

Set the API_LEVEL to 14.

Fix themes/night.css for iOS browsers

Somehow the image filters order matters for iOS browsers (Chrome, Safari), so
grayscale filter is not applied if -webkit-filter is not the last filter in
list.

See merge request !34

Somehow the image filters order matters for iOS browsers (Chrome, Safari), so
grayscale filter is not applied if -webkit-filter is not the last filter in
list.

German translation



See merge request !33

Pass the value of cache_images to plugins in HOOK_ARTICLE_FILTER.

Adds the `$cache_images` value to the `$article['feed']` array before calling HOOK_ARTICLE_FILTER. Allows plugins to know whether images will be cached in case they want to manage them in one way or another.

See merge request !32

Remove href attribute if it executes JavaScript.

Security update to prevent A tags with a `javascript:` href from actually executing the JavaScript.

See merge request !31

Only strings need 4-byte filtering.

Things like booleans, integers, etc. can be excluded as only strings have 4-byte characters.

Keeps the data types consistent.

See merge request !30