Disable flash by default

The current flash implementation isn't great so should be disabled by
default for now.

data/camera.ui

@@ -62,7 +62,7 @@
                         <child>
                           <object class="GtkButton" id="flash-controls-button">
                             <property name="valign">start</property>
-                            <property name="icon-name">flash-enabled-symbolic</property>
+                            <property name="icon-name">flash-disabled-symbolic</property>
                             <style>
                               <class name="circular"/>
                             </style>

src/main.c

@@ -53,7 +53,7 @@ static int exposure;
 static bool has_auto_focus_continuous;
 static bool has_auto_focus_start;
 
-static bool flash_enabled = true;
+static bool flash_enabled = false;
 
 static bool setting_save_dng;