Forward Right-Ctrl to the device

Only capture Left-Ctrl for scrcpy shortcuts, so that Right-Ctrl can be
forwarded to the device.

Fixes #555 <https://github.com/Genymobile/scrcpy/issues/555>

app/scrcpy.1

@@ -203,52 +203,54 @@ Default is 0 (automatic).\n
 
 .SH SHORTCUTS
 
+\fBLCtrl\fR is the left Ctrl key (the right Ctrl key is forwarded to the device).
+
 .TP
-.B Ctrl+f
+.B LCtrl+f
 Switch fullscreen mode
 
 .TP
-.B Ctrl+Left
+.B LCtrl+Left
 Rotate display left
 
 .TP
-.B Ctrl+Right
+.B LCtrl+Right
 Rotate display right
 
 .TP
-.B Ctrl+g
+.B LCtrl+g
 Resize window to 1:1 (pixel\-perfect)
 
 .TP
-.B Ctrl+x, Double\-click on black borders
+.B LCtrl+x, Double\-click on black borders
 Resize window to remove black borders
 
 .TP
-.B Ctrl+h, Home, Middle\-click
+.B LCtrl+h, Home, Middle\-click
 Click on HOME
 
 .TP
-.B Ctrl+b, Ctrl+Backspace, Right\-click (when screen is on)
+.B LCtrl+b, Ctrl+Backspace, Right\-click (when screen is on)
 Click on BACK
 
 .TP
-.B Ctrl+s
+.B LCtrl+s
 Click on APP_SWITCH
 
 .TP
-.B Ctrl+m
+.B LCtrl+m
 Click on MENU
 
 .TP
-.B Ctrl+Up
+.B LCtrl+Up
 Click on VOLUME_UP
 
 .TP
-.B Ctrl+Down
+.B LCtrl+Down
 Click on VOLUME_DOWN
 
 .TP
-.B Ctrl+p
+.B LCtrl+p
 Click on POWER (turn screen on/off)
 
 .TP
@@ -256,39 +258,39 @@ Click on POWER (turn screen on/off)
 Turn screen on
 
 .TP
-.B Ctrl+o
+.B LCtrl+o
 Turn device screen off (keep mirroring)
 
 .TP
-.B Ctrl+Shift+o
+.B LCtrl+Shift+o
 Turn device screen on
 
 .TP
-.B Ctrl+r
+.B LCtrl+r
 Rotate device screen
 
 .TP
-.B Ctrl+n
+.B LCtrl+n
 Expand notification panel
 
 .TP
-.B Ctrl+Shift+n
+.B LCtrl+Shift+n
 Collapse notification panel
 
 .TP
-.B Ctrl+c
+.B LCtrl+c
 Copy device clipboard to computer
 
 .TP
-.B Ctrl+v
+.B LCtrl+v
 Paste computer clipboard to device
 
 .TP
-.B Ctrl+Shift+v
+.B LCtrl+Shift+v
 Copy computer clipboard to device (and paste if the device runs Android >= 7)
 
 .TP
-.B Ctrl+i
+.B LCtrl+i
 Enable/disable FPS counter (print frames/second in logs)
 
 .TP