Add proper tags support

[witchy-mutant]

https://twitter.com/ChristosMatskas/status/664749426037141504

Christos Matskas:
"I know I'm asking much but is it possible to have tags? Sometimes the conf name doesn't describe the tech stack etc"

[ptrstpp950]

@mihcall we have this already. Maybe we should close this issue?

[witchy-mutant]

I probably meant making them visually distinctive and add ability to click on tags to filter results. Just ideas. It's probably good for now.

[cmatskas]

I like the filtering by tags, but we need to standardize them as at the moment it's a free for all. Any text goes and, to be honest, I sometimes struggle to find the appropriate tag to attach to a CfP

[mpraglowski]

If we "standardize" tags it won't be tags anymore, this will become category choosen from some list.

[kkokosa]

StackOverflow (StackExchange in general) has very nice, standarized tags we all know - I would go into such direction, both conceptually and visually.

[cmatskas]

Agreed with @kkokosa :)