install codegenTemplates

[pmolodo]

Description of Issue

the codegenTemplates directory is not installed in the bin dir, so any time "usdGenSchema" is run, it needs to be pointed at a source-code checkout (or the directory needs to be manually copied)

This issue is referenced in #158, but I felt it deserved it's own issue.

Steps to Reproduce

1. Do a default / fresh usd build + install
2. cd to a directory with a valid schema.usd file
3. Run usdGenSchema
4. It will error if the "-t/--templates" arg is not set, because the default templates are not installed in ${USD_INSTALL_ROOT}/bin/codegenTemplates

[meshula]

+1 This would for sure be a boon to people developing plugins, but relying on a distributed package.

[jtran56]

Filed as internal issue #146333.

[chadrik]

Are there any complicating factors to this issue or is it as simple as adding some install commands to cmake?