[FEATURE] sap.m.BusyDialog: Add HCB styles

1. Add box-shadow around the dialog to be the
   same as the one from the Dialog control.
2. Add margin to the button in the footer.
3. Add a box around the icon/svg used for
   busy indicator.
4. Add borders to the title and footer.
5. Fix units to rem.
6. Change border radius to 4px.

Change-Id: Iee0cad1b7842f733dc0a62d6d563d413e1125f9b
Signed-off-by: Deyan Yanakiev <deyan.yanakiev@sap.com>
Merge "[FEATURE] sap.m.BusyDialog: Add HCB styles"