Add tags to task

Add searchable tags to task schema. Two ways of doing this:

## Relational database
Basically, two new schemas `Tags` and `TagDefinitions` would be added. `Tags` would relate tag ids to task ids. `TagDefintions` would store the definitions to task ids.
### Pros:
* Easy updating of tag definitions
* Fastest querying

### Cons:
* Extra database, might get big depending on number of tasks/tags
## Add `tags` key in task schema
Just add an array to the task schema
### Pros:
* Easy updating of tag definitions
* Fast querying
*
### Cons:
* Can't update/delete tags very easily
* Can't see all tags very easily