.lottie extension should be supported on Lottie objects

[vchelaru]

When adding a lottie file with the .lottie extension, the following popup appears:

Instead, the file should be loaded correctly.

Also, note that the popup does say "textures" but this is incorrect since source file can be textures, .achx, lottie animations, and .svgs depending on the context.

A better error message should be shown.