New command: `knit tag find`

User should remember "What Tags are defined?" now.

User should be able to search Tags in Knitfab.

# Design Issue

- More informations except its key:value?
  - How many Data have this Tag?
  - How many Inputs/Outputs have this Tag?
  - co-occurance with other Tags
  - and more/less?

If WebAPI returns co-ocuurance, it is possible that client draw Tags cloud.