www: miscellaneous mustache updates

1. Converted /dashboards and /threadz into mustache templates. In /threadz,
   I tried to defer as much work as possible outside the lock, since it must
   be taken in write mode to create a new thread. While I was there I added
   "fancy tables" to /threadz; /dashboards remains visually unchanged.
2. In /tablets, changed the handling of tablet links. In doing so, all links
   (except for the main template) are now in templates instead of in code.

Screenshots: https://imgur.com/a/AOTQuH4

Change-Id: Idb97a9e3bbefb8ee607638af6e069959c5354225
Reviewed-on: http://gerrit.cloudera.org:8080/14473
Tested-by: Kudu Jenkins
Reviewed-by: Andrew Wong <awong@cloudera.com>
Reviewed-by: Alexey Serbin <aserbin@cloudera.com>
7 files changed