Joystick to keyboard mapping and secondary BBC joystick support

[monkeyman79]

• Assigning host joystick axes and buttons to BBC keyboard (up to 4 joysticks or gamepads separately).
• New human readable file format for joystick to keyboard mapping (see Documents/JoystickMap.txt)
• Changed joystick API from WinMM to DirectInput
• Display joystick names in menu
• Option to automatically load image-specific joystick mapping file (same as disk name, but with .jmap extension)
• Added "unassign" to keyboard and joystick mapping dialog
• Highlight assigned keys in joystick mapping dialog
• Added second BBC joystick support
• Select PC joystick and axes for each BBC joystick
• Save joystick order in preferences file
• Added "Change Joystick Order" dialog
• Added Joystick Sensitivity parameter
• Change Digital Mousestick handling
• Map additional joystick buttons to analogue port PB0 and PB1
• Removed "Basic Hardware Only" option
• Unmute when keyboard mapping dialog is closed
• Separate fire buttons on BBC joystick

Another redo of PR #87. Rebased branch because previous one became messy.