Add search feature

[frederikheld]

AS user
I WANT TO find contents in title, description, card text and tags
SO THAT I don't need to click trough all cards to find something (or find out that it doesn't exist).

[frederikheld]

Idea:

• New module "search-indexer", that can be run during build and builds up the search indexer (this package looks like a good option for this: https://github.com/nextapps-de/flexsearch)
• Add search bar with auto-complete to interface (in header). FlexSearch comes with an example for auto complete.

Open question: Where to place the search index?
A) Deliver the whole search index with the website
Pros:

• No server requests needed for searching (faster, works offline)
  Cons:
• Might be a huge download (slows down initial page load > could be done async though)
• It's more difficult to get feedback on what people are looking for (and would require server requests as well, but no negative side effects for the user if the server is not available)

B) Run a microservice that answers search requests
Pros:

• Can be scaled as needed
• Easier to get feedback on what people are looking for
  Cons:
• Search function not available if offline (but most probably the whole server will go down, so no microservice would be available)

I'm in favor of B right now...