CLI Launch (#366)

* Scanpy engine now required

Without the --engine param we need to error if scanpy engine cannot be imported rather than waiting for all engines

* CLI options and help matches proposal

(but not all options hooked up yet)

* Flesh out top level args

* Move computation args to engine

* CLI input file (#374)

* Fix test command

(tests still won't work)

* Input is file instead of directory
- also renamed example file

* Csweaver/debug (#376)

* Respect debug flag for logging flask calls

* Add loading messages

* max categories (#377)

* Add max categories

* Rename max_categories to category_selection_limit

* ensure whole numbers

server/app/driver/driver.py

@@ -12,10 +12,11 @@ Sort order for methods
 
 class CXGDriver(metaclass=ABCMeta):
 
-    def __init__(self, data, layout_method=None, diffexp_method=None):
+    def __init__(self, data, layout_method=None, diffexp_method=None, category_selection_limit=100):
         self.data = self._load_data(data)
         self.layout_method = layout_method
         self.diffexp_method = diffexp_method
+        self.category_selection_limit = category_selection_limit
         self.cluster = None
 
     @property