Icinga DB Support

[nilmerg]

My basic host cube implementation can be found here. (Requires https://github.com/Icinga/ipl-sql/pull/48)

The main differences compared to #64 are:

• The CubeRenderer classes have moved to their own namespace: Icinga\Module\Cube\CubeRenderer
• The classes DbCube and ZfSelectWrapper have moved to the namespace Icinga\Module\Cube\Ido
• The available facts are fetched from customvar_flat instead of customvar
• The queries are assembled by making use of ipl-orm's capabilities

Things to change:

• I consider the class IcingaDbHostStatusCube to be final, generally. But class IcingaDbServiceStatusCube isn't implemented yet
• The class IcingaDbCube mostly consists of the method fetchAll(). It doesn't differentiate between inner, full and rollup queries, which it should IMHO
• Icinga\Module\Cube\IcingaDb\CustomVariableDimension::addToCube() needs to be implemented. Note my todo's in method IcingaDbCube::fetchAll()
• A hook for action links is required, it should require to implement this method:

  /**
  * Create additional action links for the given cube
  * 
  * @param Icinga\Module\Cube\IcingaDb\IcingaDbCube $cube
  * 
  * @return ipl\Web\Widget\Link[]
  */
  createActionLinks(Icinga\Module\Cube\IcingaDb\IcingaDbCube $cube)