[all] Massive restructuring of SDK

[dayeol]

This commit changes the directory structure to be more sane.

• Use CMake for hello and hello-native examples Remove Makefile and vault.sh Remove rts and let CMake handle the runtime with ExternalProject_add
• Directory lib/app/include --> include/app
• Directory lib/host/include --> include/host
• Directory lib/edge/include --> include/edge
• Directory lib/verifier/include --> include/verifier
• Directory common/include --> include/common
• Directory lib/app/src --> src/app
• Directory lib/host/src --> src/host
• Directory lib/edge/src --> src/edge
• Directory lib/verifier/src --> src/verifier
• Directory common/src --> src/common

This change completely separates the source and the build files. Also, it makes it wildly easier to "install" the headers and the libraries to a designated directory configured with a CMake flag, OUTPUT_DIR. Now, KEYSTONE_SDK_DIR should point to this "install" directory instead of the source directory. Thus, it may require runtime and keystone repo updates.

[dkohlbre]

README is currently inaccurate, should be updated in this PR. We can update the other documentation in the main Keystone pr.

[dkohlbre]

I'm also not sure what the different tests/ and examples/tests/ etc directories are. We can have both examples/ and tests/ but they should contain distinct things.

[dayeol]

They are containing distinct things. examples/tests contains the test binaries that we used to use, tests contains googletest-based unit tests.