MODIS historical image layers plugin

The OnEarth WMS has 250m/pixel daily mosaics going back for two years. This is a plugin to choose and view those layers directly in WW.

Usage
To use, load the plugin, then choose "MODIS historical layers" from the Plugins menu to load the form. Create a list of dates that you want to view by choosing a date in the calendar menu and clicking the "Add date" button. When you have chosen all the dates you want, decide whether you want the daily aqua or terra layers and click the "Add all to layer manager" button to add them to the LM.

You can add more layers by clearing the date list, choosing more dates, and clicking the "Add all to layer manager" button again. The layers aren't added permanently, they will disappear when WW restarts.

To add dates permanently to the LM, choose the dates, add them to the LM, then copy the "temp.xml" file in "\Plugins\MODIS historical\" to "\Config\Earth\". The temp.xml file will only contain the dates that were added the last time you clicked the "Add all" button.

The "Clear all from LM" is buggy, it may or may not work. The layers can be cleared by restarting WW or reloading Earth.

The data goes back two years, but because the server was down from Dec 7 to Dec 16, there are no images available for those days.

TODO

 * Find a better way to choose whether individual layers are added permanently or temporarily.
 * Fix the clear button.