Slave info: un-revert, fix a bug, add a box

This is master-branch patch.

This patch:
* reverts commit f518276b3a6e88a6b079a4e2661a152087eedd15,
    which itself had reverted 1c5973413aa3b7e5f2f197b488cd58206b7ac057,
      which was the merge of branch SlaveInfo.
* Fixes a minor bug in SetSlaveInfo
* Adds a box to the buildslave web page to display the slaveinfo dictionary, just as "properties" show on a Build page (the code was pretty much copy-pasted)