Walter build using shared libraries

[frenchdog]

At the beginning of the Walter project, we decided to go the static way to avoid libraries conflicts with the ones included in DCCs (mainly boost and tbb). However, it should be possible to use shared libraries if we spend enough time on the problem :). There are some benefits with static libs, but also issues. For example if Walter was using shared libraries, its build system could be much smaller (and then easier to port to Windows). You could just link with your already installed OpenEXR, Alembic, etc... libraries. Also some part of Walter could be more easy to merge in USD main repo for example. At Rodeo FX this is something we would like to do, but since our static build system is working for us, it is not the top priority (we are focusing on our USD pipeline currently). So I think it would be a very good idea to start working on the "shared library option" as an open project first. The starting point would be to link walterUsdExtras library dynamically with USD libraries. Walter USD schemas, resolver and file format plugins will need to be installed as standard USD plugins. Finally, we need to remember that some dependencies (currently statically build) are patched. So even when we will be able to link dynamically, the Walter build system will still need to include the build of a couple of patched libraries (thinking about Boost and Alembic ones for example).