Add update manager

[FelixWolf]

Wowe now people can be notified when there is a update available!

Despite the name, this doesn't do automated updates. Depending on who you ask, this will be disappointing or a benefit.

IMPORTANT

indra/newview/app_settings/settings_alchemy.xml needs to be changed! Specifically the AlchemyUpdateURL key. Which currently points to my server for testing.

alsetup.xml syntax

The correct XML format is documented in a comment at indra/newview/alupdatemanager.cpp, which at the time is currently:

<llsd>
  <map>
    <!-- Put all entries in a sub map called "channels", in case we want to
         include something else shared between all channels. -->
    <key>channels</key>
    <map>
      <key>Alchemy Test</key>
      <map>
        <!-- Build ID, viewer checks if this is newer -->
        <key>build</key>
        <integer>123456</integer>

        <!-- Full version number -->
        <key>version</key>
        <string>1.2.3.45678</string>

        <!-- A URL to the download page -->
        <key>download</key>
        <string>Page to open in browser when user clicks "download"</string>

        <!-- A optional message -->
        <key>message</key>
        <string>Coyito was here!</string>
      </map>
    </map>
  </map>
</llsd>

This adds the following automated update check:

1. Disable automatic update checks if AlchemyUpdateEnableAutoCheck is set to true (This is configurable in the "Setup" preferences tab. A "Privacy Policy" link is also included).
2. Upon start up, check as soon as possible for a update.
3. After the first check, check every AlchemyUpdateCheckFrequency seconds (Default is 3600 seconds, or 1 hour). This can also be set to 0 to not do timed checks (I.E. Only check on start up).
4. If the user chooses "Ignore" on the dialog, it will suppress update notifications for that session. It is not possible to ignore a entire update because we only support the latest version of each channel IIRC.
5. If a update is detected on the login screen, the user is notified via a pop up.
6. If a update is detected while logged in, the user is notified via a system toast.

New alchemy_settings.xml keys:

• AlchemyUpdateURL - (string) path to update XML url.
• AlchemyUpdateEnableAutoCheck - (bool) If update checks are enabled.
• AlchemyUpdateCheckFrequency - (float) How often in seconds to check for updates.

New notifications:

• AlchemyUpdateAlert - Popup notification for login screen
• AlchemyUpdateToast - Toast notification for in-world

New preference settings:

• Setup > Software Updates - A option to disable notification checks (for privacy concerned residents). Privacy policy is also linked next to this.
• Setup > Software Updates - A "Check now" button as well as a last checked timer.