Download bsp files at build time and remove from git lfs about basilisk

[schaubh]

Howdy @patkenneally , thanks for posting this issue and thoughts on this. Some quick thoughts and questions on my side:

• As the CMAKE would be pulling the large Spice files, this is only done once I assume. When a clean build is requested we delete the dist3 folder, but the spice file would remain I assume and would not need to be downloaded again? I'm 99% sure the answer is yes reading up on this, but wanted to check
• As we keep improving the build system of BSK, a goal of mine is to readily be able to build BSK when not connected to the internet. I'm assuming all dependencies are already downloaded and built. I would like to be able to do clean test builds while on a plane. For this requested feature, if there is a way to make this work where it doesn't need internet if the file already exists, that would be a huge plus to me at least. :-) Right now I can't do a clean build if there is no internet connection.
• I agree with your statement that this would improve the BSK install, configure and build process by not having the new user also having to learn to setup git-lfs. I'm excited to see this change implemented.
• Regarding the web url for the Spice files, we could put them on a private server. My first choice, however, would be to use the official server. With the many BSK dependencies we already have to do some occasional maintenance to keep the builds working with the latest conan repos, python package version, etc. If the link doesn't work, it would be nice for the CMAKE to error with a verbose message telling the user what happened, and if needed they can download the required file from the Spice web page and drop it into the BSK folder.