CP-8866:Develop for Resource Statistic Feature on XenCenter

Based on the requirements draft and discussed solution, develop the prototype for Resource Statistic Feature part on XenCenter, that is, provide the export to Excel and CSV functionality with required data sets,by accessing the XenCenter cache.
Signed-off-by: Cheng Zhang <cheng.zhang@citrix.com>
MAINWINDOW_EXPORT_POOL_RESOURCE_LIST should have a hotkey for keyboard users. 'x' is unused on this menu, so I suggest
<value>E&amp;xport pool resource list</value>