This resolves a PBD vs ARDOUR namespace error for some compilers:
```
error: reference to 'microseconds_t' is ambiguous
libs/pbd/pbd/microseconds.h:29:19: error: candidates are: typedef uint64_t PBD::microseconds_t
libs/ardour/ardour/types.h:81:29: error: typedef PBD::microseconds_t ARDOUR::microseconds_t
```
* fixes Master Fader Touch button in the Mackie;
* implements a MasterFaderTouch global button;
* removes unused MackieControlProtocol::_transport_previously_rolling property;
* implements DeviceInfo::get_global_button() method;
* creates GlobalButtonsInfo and StripButtonsInfo types in DeviceInfo;
* implements Surface::_last_master_gain_written property to help master fader feedback;
* makes Surface respect _mcp.device_info().strip_cnt() to create master fader and when connecting signals for strips and master fader instead of using hardcoded 8;
* removed a few unnecessary updates in Surface::turn_it_on();
* included master_gain_changed() in Surface::periodic();
* implemented MackieControlProtocol::master_fader_touch_press and
* MackieControlProtocol::master_fader_touch_release;
git-svn-id: svn://localhost/ardour2/branches/3.0@12631 d708f5d6-7413-0410-9779-e7cbd77b26cf
