Fix warnings when compiling against GCC 5.4

correct type to avoid compiler warning

Allow for use of either 128x64 or 128x32 displays

Support for custom font table look-up function

Fixes the following warnings when compiling using GCC 5.4:

    CXX OLEDDisplayUi.o
    ./OLEDDisplayUi.cpp: In member function 'void OLEDDisplayUi::drawFrame()':
    ./OLEDDisplayUi.cpp:284:48: error: 'y1' may be used uninitialized in this function [-Werror=maybe-uninitialized]
	    x *= dir; y *= dir; x1 *= dir; y1 *= dir;
						    ^
    ./OLEDDisplayUi.cpp:284:37: error: 'x1' may be used uninitialized in this function [-Werror=maybe-uninitialized]
	    x *= dir; y *= dir; x1 *= dir; y1 *= dir;
					 ^
    ./OLEDDisplayUi.cpp:284:26: error: 'y' may be used uninitialized in this function [-Werror=maybe-uninitialized]
	    x *= dir; y *= dir; x1 *= dir; y1 *= dir;
			      ^
    ./OLEDDisplayUi.cpp:284:16: error: 'x' may be used uninitialized in this function [-Werror=maybe-uninitialized]
	    x *= dir; y *= dir; x1 *= dir; y1 *= dir;
		    ^
    ./OLEDDisplayUi.cpp: In member function 'void OLEDDisplayUi::drawIndicator()':
    ./OLEDDisplayUi.cpp:393:35: error: 'y' may be used uninitialized in this function [-Werror=maybe-uninitialized]
	   this->display->drawFastImage(x, y, 8, 8, image);
				       ^
    ./OLEDDisplayUi.cpp:393:35: error: 'x' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    ./OLEDDisplayUi.cpp:387:7: error: 'posOfHighlightFrame' may be used uninitialized in this function [-Werror=maybe-uninitialized]
	   if (posOfHighlightFrame == i) {
	   ^
    cc1plus: some warnings being treated as errors

Fix the following warnings, seen when compiling with GCC 5.4:

    CXX OLEDDisplay.o
    ./OLEDDisplay.cpp: In member function 'void OLEDDisplay::drawStringInternal(int16_t, int16_t, char*, uint16_t, uint16_t)':
    ./OLEDDisplay.cpp:381:10: error: enumeration value 'TEXT_ALIGN_LEFT' not handled in switch [-Werror=switch]
       switch (textAlignment) {
	      ^
    ./OLEDDisplay.cpp: In member function 'void OLEDDisplay::drawInternal(int16_t, int16_t, int16_t, int16_t, const char*, uint16_t, uint16_t)':
    ./OLEDDisplay.cpp:722:13: warning: unused variable 'yScreenPos' [-Wunused-variable]
	 int16_t yScreenPos = yMove + yOffset;
		 ^
    ./OLEDDisplay.cpp: In member function 'void OLEDDisplay::drawXbm(int16_t, int16_t, int16_t, int16_t, const char*)':
    ./OLEDDisplay.cpp:361:19: error: 'data' may be used uninitialized in this function [-Werror=maybe-uninitialized]
	     data >>= 1; // Move a bit
		       ^
    cc1plus: some warnings being treated as errors

Fix platforms in library.json

fix typo in integer type (causes compile error)

`warning: narrowing conversion of '128' from 'int' to 'const char' inside { } [-Wnarrowing]`

Closer to middle vertical align

Make OLEDDisplay.display() an abstract function

Implement setLoadingDrawFunction. Fixes #102

Without the `= 0` declaration, compiling with RTTI enabled fails.
See http://stackoverflow.com/a/307427/1880101 for an explanation.

Also use closer indicator spacing when using indicators on left or
right of screen with less than 64 height.