Cache UIPrinter (#128)

* Cache UIPrinter

This speeds up printing time from 25 seconds to < 5

* Switching to isEqualToString

src/ios/APPPrinter.h

@@ -25,6 +25,9 @@
 
 @interface APPPrinter : CDVPlugin <UIWebViewDelegate>
 
+// this is used to cache the uiprinter making repeated prints faster
+@property (nonatomic) UIPrinter *previousPrinter;
+
 // Find out whether printing is supported on this platform
 - (void) check:(CDVInvokedUrlCommand*)command;
 // Displays system interface for selecting a printer

src/ios/APPPrinter.m

@@ -195,7 +195,14 @@
                printer:(NSString*)printerId
 {
     NSURL* url         = [NSURL URLWithString:printerId];
-    UIPrinter* printer = [UIPrinter printerWithURL:url];
+    
+    // check to see if we have previously created this printer to reduce printing/"contacting" time
+    if(self.previousPrinter == nil || ![[[self.previousPrinter URL] absoluteString] isEqualToString: printerId]) {
+        self.previousPrinter = [UIPrinter printerWithURL:url];
+    }
+    
+    UIPrinter* printer = self.previousPrinter;
+    
     
     [controller printToPrinter:printer completionHandler:
      ^(UIPrintInteractionController *ctrl, BOOL ok, NSError *e) {