Making the "tag" feature functional

[juliakramer]

Currently, the "add" tags button doesn't work and therefore tags cannot be added. See edit screen image below:

• Make "add" tags button work
• Make added tags visible on the method or case study's sidebar (see image below)
  
• Make the tags clickable, similar to how we currently are able to click on a method's "characteristics" to show all other methods with the same characteristic. So, if you click a method's tag that says "sustainable design", all other methods and case studies tagged with "sustainable design" will show up
• Make the tags searchable, so that if I keyword search "sustainable design", all methods or case studies tagged as "sustainable design" show up