Allow building files while setup runs in background

[suoto]

When Vim is opened, vim_client.VimhdlClient.setup is run in a thread and calls to vim_client.VimhdlClient.buildByPath are locked until setup completes.

• Implement a database inside project_builder.ProjectBuilder, taking into account errors (currently this is ignored)
• Allow vim_client.VimhdlClient.buildByPath to be run while vim_client.VimhdlClient.buildByDependency is active
• Shell calls called by compilers.base_compiler.BaseCompiler must be queued to avoid consistency errors by the compiler (it may not handle multiple threads accessing its internal DB)

Expected result:

• Open Vim with nothing built (this will trigger background build)
• While the build is running, build the current file
  • If dependencies have already been built, build it
  • If dependencies haven't been built, warn the user (don't wait until dependencies are met)

[suoto]

Issue has been implemented as of c936db8. Misc crashes fixed after that due to poor exception handling inside threads but most have been fixed as well.