Update Open Enclave SDK package configuration

[CodeMonkeyLeet]

This issue tracks updating the Open Enclave SDK package configuration before publishing it for Public Preview. This is a prerequisite for #48.

Per @mikbras:

Change install directory to /opt/openenclave. Currently OE installs under /usr/local/*, which puts our
components on the default path. The samples were working on my machine and failing on Anita’s
machine because they were finding /usr/local/bin/oegen rather than the one in our build directory.
Most Microsoft projects place these kinds of tools under /opt for this reason.

mikras> After further consideration, I would leave the install prefix as /usr/local. If we don't install here, the user will have to manage:

• PATH
• PGK_CONFIG_PATH
• The search path for libraries.

Also note that some of the paths in the source tree are not fully pathed, so the developer will encounter certain problems (like depending on the installed version of oesign rather than the version in the source tree).

Other changes in this vein:

• Remove oegen and other internal tools from being published
• Remove internal headers from being published

[herveyw-msft]

@CodeMonkeyLeet This seems wrong to me, especially just to fix a build problem. The file system standard says /usr/local is for administrator installed packages, /opt is for optional packages.

[CodeMonkeyLeet]

Resolved, also see additional cleanup PRs #863 and #867 for the v0.4.0 SDK release