Remove Old Multi-Client Code / Refactoring (#13)

* Remove a lot of old code from render_queue regarding clients

* More code cleanup

* More code cleanup

* Move everything around

* Minor log change

lib/engines/base_engine.py

@@ -0,0 +1,46 @@
+import logging
+import os
+import subprocess
+
+logger = logging.getLogger()
+SUBPROCESS_TIMEOUT = 5
+
+
+class BaseRenderEngine(object):
+
+    install_paths = []
+    supported_extensions = []
+
+    @classmethod
+    def name(cls):
+        return cls.__name__.lower()
+
+    @classmethod
+    def renderer_path(cls):
+        path = None
+        try:
+            path = subprocess.check_output(['which', cls.name()], timeout=SUBPROCESS_TIMEOUT).decode('utf-8').strip()
+        except subprocess.CalledProcessError:
+            for p in cls.install_paths:
+                if os.path.exists(p):
+                    path = p
+        except Exception as e:
+            logger.exception(e)
+        return path
+
+    @classmethod
+    def version(cls):
+        raise NotImplementedError("version not implemented")
+
+    @classmethod
+    def get_help(cls):
+        path = cls.renderer_path()
+        if not path:
+            raise FileNotFoundError("renderer path not found")
+        help_doc = subprocess.check_output([path, '-h'], stderr=subprocess.STDOUT,
+                                           timeout=SUBPROCESS_TIMEOUT).decode('utf-8')
+        return help_doc
+
+    @classmethod
+    def get_output_formats(cls):
+        raise NotImplementedError(f"get_output_formats not implemented for {cls.__name__}")