Fix compiler warnings

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

OLEDDisplay.cpp

@@ -353,7 +353,7 @@ void OLEDDisplay::drawFastImage(int16_t xMove, int16_t yMove, int16_t width, int
 
 void OLEDDisplay::drawXbm(int16_t xMove, int16_t yMove, int16_t width, int16_t height, const char *xbm) {
   int16_t widthInXbm = (width + 7) / 8;
-  uint8_t data;
+  uint8_t data = 0;
 
   for(int16_t y = 0; y < height; y++) {
     for(int16_t x = 0; x < width; x++ ) {
@@ -388,6 +388,8 @@ void OLEDDisplay::drawStringInternal(int16_t xMove, int16_t yMove, char* text, u
     case TEXT_ALIGN_RIGHT:
       xMove -= textWidth;
       break;
+    case TEXT_ALIGN_LEFT:
+      break;
   }
 
   // Don't draw anything if it is not on the screen.

OLEDDisplay.h

@@ -250,7 +250,7 @@ class OLEDDisplay : public Print {
     virtual void sendCommand(uint8_t com) {};
 
     // Connect to the display
-    virtual bool connect() {};
+    virtual bool connect() {return true;};
 
     // Send all the init commands
     void sendInitCommands();