Initial set up for Ghost Inspector integration tests.

Adds a CircleCI integration for Ghost Inspector
(https://ghostinspector.com), a headless browser testing SaaS. The
README is updated with details about how to run GI locally.

Removes the bootstrap setup for Selenium testing with BrowserStack.

.secrets.baseline

@@ -3,7 +3,7 @@
     "files": "^.secrets.baseline$",
     "lines": null
   },
-  "generated_at": "2019-10-03T14:34:50Z",
+  "generated_at": "2019-10-14T19:14:26Z",
   "plugins_used": [
     {
       "base64_limit": 4.5,
@@ -40,6 +40,13 @@
         "is_verified": false,
         "line_number": 156,
         "type": "Secret Keyword"
+      },
+      {
+        "hashed_secret": "81b127e2222d9bfc4609053faec85300f7525463",
+        "is_secret": false,
+        "is_verified": false,
+        "line_number": 244,
+        "type": "Secret Keyword"
       }
     ],
     "alembic.ini": [
@@ -153,24 +160,6 @@
         "type": "Private Key"
       }
     ],
-    "tests/acceptance/conftest.py": [
-      {
-        "hashed_secret": "bf21a9e8fbc5a3846fb05b4fa0859e0917b2202f",
-        "is_secret": false,
-        "is_verified": false,
-        "line_number": 48,
-        "type": "Basic Auth Credentials"
-      }
-    ],
-    "tests/fixtures/chain/make-chain.sh": [
-      {
-        "hashed_secret": "bad2e396920ce37fe53fc291f90b130d915375fb",
-        "is_secret": false,
-        "is_verified": false,
-        "line_number": 35,
-        "type": "Secret Keyword"
-      }
-    ],
     "tests/forms/test_validators.py": [
       {
         "hashed_secret": "260408f687da9094705a841acda9b029563053ee",
@@ -194,7 +183,7 @@
         "hashed_secret": "e4f14805dfd1e6af030359090c535e149e6b4207",
         "is_secret": false,
         "is_verified": false,
-        "line_number": 651,
+        "line_number": 656,
         "type": "Hex High Entropy String"
       }
     ]