This patch add the notion of groups to the project

A group is just a container of dashboards.
This new notion introduce the possibility of filter the dashboards
by group, linking a dashboard with the others in the group, etc...
Those features will be commited later.
In this commit :
	- Add a group
	- Edit a group
	- Delete a group
There is also the script that create the new sql table and, if the base
is already created, a script that add the column "group_id"
in the dashboard table.
Add a dashboard in a group and filter list by grps

Add the possibility of classing a dashboard in a group in the edition page
In the list page, the user can now apply a filter and display only
the dashboards of a group
Patch : import and export dashboards in JSON

The user can export a simple dashboard or a selection of dashboards.
The user can also import a JSON file that contains one or several
dashboards which will be added into the group that is currently filtered.
(If there is no filter, the dashboards will be added into the default group)
Evolutions in the page "view_dashboard.php"

Two div (that can be hidden) were added :
	- The first one contains several options :
		- Usefull values of "from"
		- Frequent values for the size of the graph
		- Different colors for text or background of the graph
	- The second contains the links of the other dashboards in the group
The options are defined in some arrays in "dashboard.php"

This commit also fixes the display of the columns
upgrading twitter bootstrap to version 2.3.2
porting style and parameters to bootstrap 2.3.2
The user can clone a graph into another dashboard
Mass export  : highlights the selected lines
Add CSS class and CSS style for "view_dashboard"

This commit also contain a little fix for the submit button of the mass export:
the css class "btn" was added.