[server][FaceRest] Generalize addHostgroupsMap() so that other methods can use it.
[server][DBClientTest] Use const & for an input parameter.
[server][Params] User a defined type to improve change tolerability.
[server][FaceRest] Show information by host groups on the overview API.
[client][Dashboard] Replace multibyte-spaces with single spaces.
Revert "[client][Dashboard] Replace multibyte-spaces with single spaces."

This reverts commit 6e85190b99c884085072da5d04790988a1d08cb0.

The multibyte spaces are for adjusting the width of bar chart.
This patch shortens it. As a result, it makes the layout ugly.
[client][Dashboard] Fix a bug that breaks a table layout due to a miss of a <tr> tag.