Added base class AIStateMachine.

This is the skeleton needed to implement classes that can be reused and
work together, which can perform asynchronous tasks (read: need to wait
for certain events before they can continue).

An example would be the task of waiting for a given inventory folder to
be read. This could then be used to improve the builtin AO
(automatically reading that folder when a notecard is dropped, and
continuing when the whole folder is read).

It's first use will be communication with a filepicker that runs
in a plugin.

indra/newview/app_settings/settings.xml

@@ -11382,6 +11382,17 @@
       <key>Value</key>
       <integer>0</integer>
     </map>
+    <key>StateMachineMaxTime</key>
+    <map>
+      <key>Comment</key>
+      <string>Maximum time per frame spent executing AIStateMachine objects, in miliseconds</string>
+      <key>Persist</key>
+      <integer>1</integer>
+      <key>Type</key>
+      <string>U32</string>
+      <key>Value</key>
+      <integer>20</integer>
+    </map>
     <key>StatsAutoRun</key>
     <map>
       <key>Comment</key>