Add (restore) link to Matlab version of PlantTracer to home page

[sbarber2]

Per Eric, he would like the Matlab version made available from the static site again.

[sbarber2]

Hmm, restoring the icon and link is easy enough, but I am sorry to report that the GDrive folder URL previously linked to now gives a 404. Assigning to Eric for ideas about what happened there.

[sbarber2]

Here are the names of the three files that were in that GDrive folder, according to the Wayback Machine:

PlantTracer 1.0-windows.zip
PlantTracer_Installer.exe
PlantTracer_macOS.zip

[simsong]

This is the big risk of relying on other people's data hosting.