Declare the DEV-master development version
Convert add_to_log() to the new logging architecture

This is slightly breaking the backwards compatibility. From now on,
opening the 'Manage stamps' is no longer logged as a separate 'manage
stamps' action (when legavy logging is on). Instead, the standard course
module viewed event is triggered with the property other[viewmode] set
to 'manage'. So it is stored as 'view' action in the legacy log. This
better describes the essence of the event.
Lessify the CSS styling

Simplified significantly as the default clean based theme makes the
default output acceptable.