ue4cli depends on 'pkg_resources' which prevents it from running on vanilla python

[sleeptightAnsiC]

Looks like I missed this one during #59

ue4cli still depends on package outside of vanilla python and cannot be run directly from source without it:

$ python ~/ue4cli
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/home/korn/ue4cli/__main__.py", line 1, in <module>
    from ue4cli.cli import main
  File "/home/korn/ue4cli/ue4cli/cli.py", line 2, in <module>
    from .PluginManager import PluginManager
  File "/home/korn/ue4cli/ue4cli/PluginManager.py", line 2, in <module>
    import pkg_resources
ModuleNotFoundError: No module named 'pkg_resources'

For now, I only spotted pkg_resources (provided by setuptools) which is used in two places:

1. pkg_resources.iter_entry_points
   

   ue4cli/ue4cli/PluginManager.py

   Lines 15 to 20 in fed71c1

   	# Retrieve the list of detected entry points in the ue4cli.plugins group
   	plugins = {
   	entry_point.name: entry_point.load()
   	for entry_point
   	in pkg_resources.iter_entry_points('ue4cli.plugins')
   	}

2. pkg_resources.parse_version
   

   ue4cli/ue4cli/UnrealManagerDarwin.py

   Lines 35 to 47 in fed71c1

   	def _editorPathSuffix(self, cmdVersion):
   	version = parse_version(self.getEngineVersion())
   	if version < parse_version('5.0.0'):
   	return '.app/Contents/MacOS/UE4Editor'
   	else:
   	return '.app/Contents/MacOS/UnrealEditor'
   	def _transformBuildToolPlatform(self, platform):
   	# Prior to 4.22.2, Build.sh under Mac requires "macosx" as the platform name for macOS
   	version = parse_version(self.getEngineVersion())
   	return 'macosx' if platform == 'Mac' and version < parse_version('4.22.2') else platform

First one is tricky, we have to use it for loading ue4cli-plugins which is invoked in ue4cli/cli.py.
Second one should be fairly easy to replace (I hope).

TODO:
I gotta make sure there is no more dependencies like this one and find good workaround for this.
Perhaps we can try; import pkg_resources: and load ue4cli-plugins only if said dependency is resolved.

Either way, I'll probably take this one :)

[sleeptightAnsiC]

Potential fix for 1.
This already makes it work on Windows and Linux

diff --git a/ue4cli/PluginManager.py b/ue4cli/PluginManager.py
index e157394..8df7b13 100644
--- a/ue4cli/PluginManager.py
+++ b/ue4cli/PluginManager.py
@@ -1,5 +1,14 @@
 from inspect import signature
-import pkg_resources
+from .Utility import Utility
+
+# HACK: dummy iter_entry_points in case package 'setuptools' hasn't been provided
+try:
+	from pkg_resources import iter_entry_points
+except ModuleNotFoundError as e:
+	Utility.printStderr(f'Warning: ue4cli plugins are unavailable due to: {str(e)}')
+	def iter_entry_points(unused):
+		return {}
+
 
 class PluginManager:
 	"""
@@ -16,7 +25,7 @@ class PluginManager:
 		plugins = {
 			entry_point.name: entry_point.load()
 			for entry_point
-			in pkg_resources.iter_entry_points('ue4cli.plugins')
+			in iter_entry_points('ue4cli.plugins')
 		}
 		
 		# Filter out any invalid plugins