SideBySide2: Restore some old keybindings and fix help popup

Disable reverse search, restore "?" for help popup.
Map Ctrl+F to searching in CodeMirror, map Space to PageDown.
Take Ctrl+A back from Vim mode for selecting all text.
Disable Ctrl+O in Vim keymap since it's used by some browsers.
Add explanation of key commands to help popup.

'/' still starts a CodeMirror search instead of a Gerrit one.
Jumping within Gerrit using the 'g' prefix is still not supported.

Change-Id: Id77faa4b36add35c78edfd0d7d0611279cbe7120

gerrit-gwtexpui/src/main/java/com/google/gwtexpui/globalkey/client/KeyCommand.java

@@ -24,6 +24,7 @@ public abstract class KeyCommand implements KeyPressHandler {
   public static final int M_CTRL = 1 << 16;
   public static final int M_ALT = 2 << 16;
   public static final int M_META = 4 << 16;
+  public static final int M_SHIFT = 8 << 16;
 
   public static boolean same(final KeyCommand a, final KeyCommand b) {
     return a.getClass() == b.getClass() && a.helpText.equals(b.helpText);
@@ -58,6 +59,9 @@ public abstract class KeyCommand implements KeyPressHandler {
     if ((keyMask & M_META) == M_META) {
       modifier(b, KeyConstants.I.keyMeta());
     }
+    if ((keyMask & M_SHIFT) == M_SHIFT) {
+      modifier(b, KeyConstants.I.keyShift());
+    }
 
     final char c = (char) (keyMask & 0xffff);
     switch (c) {

gerrit-gwtexpui/src/main/java/com/google/gwtexpui/globalkey/client/KeyConstants.java

@@ -32,6 +32,7 @@ public interface KeyConstants extends Constants {
   String keyCtrl();
   String keyAlt();
   String keyMeta();
+  String keyShift();
   String keyEnter();
   String keyEsc();
 }

gerrit-gwtexpui/src/main/java/com/google/gwtexpui/globalkey/client/KeyConstants.properties

@@ -10,5 +10,6 @@ thenOtherKey = then
 keyCtrl = Ctrl
 keyAlt = Alt
 keyMeta = Meta
+keyShift = Shift
 keyEnter = Enter
 keyEsc = Esc