UI: Enhancement & Fixes for Host Monitoring

Several items:

1) Tab Page Lifecycle
     Added cleanup when a page is unloaded (user switchs to other
   tab), mainly clear timers for auto refreshing (host monitoring
   and guests status).

2) Fixed bugs in kimchi.widget.Grid
     There are 2 listeners registered to document.body, and these
   listeners will accumulate when user switchs back to host page.
   Added destroy() function to unload these listeners for Grid.

3) Added confirm dialog for debug report deletion

4) Corrected Disk and Network I/O Rate Units
     Memory is in B(ytes) unit, though disk/network I/O are in B(
   ytes)/s. Added a function to allow customize unit.

v1 -> v2:
  2a) Unified units to binary prefix (Ki - 2^10, Mi - 2^20, etc.)

Signed-off-by: Hongliang Wang <hlwang@linux.vnet.ibm.com>