Added admin interface to manage channels and enabled plugins (#9)

* Added base admin login/logout flows

* Ignore local database

* Channel model

* Admin interface for channels and plugins

* Added database tests along with workflows

* Added some docstrings

* Ignore .coverage file

* Creating plugins docs WIP

* Documentation

* Black everything

* Some documentation

* Coverage for the plugins package as well

* DB Fixes

* Absolute FROM in Dockerfile

* Database and logging fixes

* Slack: Support private channels

* Added pre-commit

* black'd

* Fixed UserQuery.create

* Fixed ChannelPluginQuery.create exists call

* Added ChannelPlugin menu for debugging

* Ignore sqlite databases

* Updated contributing docs

docs/creating-a-plugin.md

@@ -0,0 +1,37 @@
+# Creating a Plugin
+
+## Example
+
+This simple "Marco Polo" plugin will answer _Polo_ to the user that say _Marco_:
+
+``` python
+# mypackage/plugins.py
+from butterrobot.plugins import Plugin
+from butterrobot.objects import Message
+
+
+class PingPlugin(Plugin):
+    name = "Marco/Polo"
+    id = "test.marco"
+
+    @classmethod
+    def on_message(cls, message, **kwargs):
+        if message.text == "Marco":
+            yield Message(
+                chat=message.chat, reply_to=message.id, text=f"polo",
+            )
+```
+
+``` python
+# setup.py
+# ...
+entrypoints = {
+    "test.marco" = "mypackage.plugins:MarcoPlugin"
+}
+
+setup(
+    # ...
+    entry_points=entrypoints,
+    # ...
+)
+```