Validate File Input

[DanielJDufour]

Describe the bug If a user tries to upload something that isn't a GeoTIFF, we should automatically check that the extension is .tif or .tiff and alert that user if it is not.

To Reproduce Steps to reproduce the behavior:

1. Go to app.geotiff.io
2. Click on choose file
3. Select a zip file
4. Click GO
5. Pretends to start loading, but never finishes

Expected behavior An alert should pop up on the screen saying only .tif and .tiff files are supported. If you have a zipped GeoTIFF file, please unzip first.

Screenshots See above

Desktop (please complete the following information):

• OS: [e.g. iOS] ChromeOS
• Browser [e.g. chrome, safari] Chrome
• Version [e.g. 22] N/A

Additional context Part of the problem is when computers hid the file extensions of files. For example, when a user tries to load a zipped tif file on Windows, Windows will hide the .zip file extension, so the file will look like a .tif file.