Turbine thrust calculation, platform external forces, !include yamls

-- Turbine class now has a properly working thrust calculation and saves the value in thrust property
-- platform class will add up total thrust from all connected turbines and save in mean_loads dictionary under 'thrust' key
	- platform mean_loads dictioanry contains 'wind', 'wave', 'current', 'thrust' keys with values defaulting to 0
-- updated !include constructor in yaml loader to work for relative paths and situations when driver file is in different folder than yaml
   - !include constructor allows user to provide a yaml file name that will be included in the main yaml when read in. See OntologySample200m.yaml topsides section for example.
-- updated examples to use !include instead of full definition for turbine raft definitions

Author: lsirkis

examples/01_Visualization/08_3D-visual_turbine.yaml

@@ -1,4 +1,5 @@
 """
+
 Simple driver file to create a RAFT model of a 2-platform array with turbines.
 This file then adds a wave spectrum to run, analyzes that case, and plots the results.
 

examples/01_Visualization/11_2D-visual_all_options.yaml

@@ -90,6 +90,8 @@ def loadYAML(filename):
 
     with open(filename) as file:
         loader = yaml.FullLoader 
+        # add a property to store the overall yaml path
+        loader.path =  os.path.dirname(os.path.realpath(filename))
         loader.add_constructor('!include',yamlInclude)
         project = yaml.load(file, Loader=loader)
         if not project:
@@ -113,14 +115,10 @@ def yamlInclude(loader, node):
     None.
 
     '''
-    # pull out f
+    # pull out file name
     file_to_include = loader.construct_scalar(node)
-    # pull out absolute path of file
-    # if os.path.isabs(file_to_include):
-    #     included_yaml = file_to_include
-    # else:
-    #     dir = 
-    included_yaml = os.path.abspath(file_to_include)
+    # combine with saved loader path property (path to overall yaml)
+    included_yaml = os.path.join(loader.path,file_to_include)#abspath(file_to_include)
     try:
         with open(included_yaml) as file:
             return(yaml.load(file,Loader=loader.__class__))