[FR]: Add a searchbar where users can search for usernames and tags

[ByteOtter]

Input field in place on layout.html however issues with it:

• [ ] Does not fill the width between the two navbar divs (also not when both margins are removed
• [ ] Does not pass entered value on to main.search

Search function in main/utils.py goals:

1. get search phrase by excluding image:true and user: blocks from search string
2. match if there is a block called user: or image:true
3. if is_user_query: return the user aswell as all posts from that user which contan the search string
4. if only_with_images retrurn only the users posts with images
5. if topic, filter returned posts by topic

In the end these are the cases and their results:	input	output
string only	all posts which contain matching strings should be returned
user:<username> flag only	matching user should be returned
topic:<topic flag only	all posts with that topic should be returned
image:true	all posts containing images shall be returned
username + string	all posts of that user containing that string should be returned
username + topic	all posts from that user which have that topic should be returned

etc etc.

[ByteOtter]

WTForms SearchField does not seem to work