Token auth (#434)

* Embed device platform information into token request

* Remove username and password from userProfile

* Display icon to show if profile has associated user token

* Remove username / password from login settings screen

* Refactor login procedure around token auth

* Refactoring

* Add profile login screen

- Username / password values are not stored
- Just to fetch api token

* Login with basic auth

* Pass profile to API when connecting

* Remove _BASE_URL accessor

- Fixes URL caching bug

* Add more context to login screen

* Add helper functions for unit tests

- Change default port to 8000 (makes testing easier with local inventree instance)

* api.dart handles basic auth now

* fix api_test.dart

* Further test improvements

* linting fixes

* Provide feedback when login fails

* More linting

* Record user details on login, and display in "about" widget

* Fix string lookup

* Add extra debug

* Fix auth values

* Fix user profile test

lib/l10n/app_en.arb

@@ -591,6 +591,15 @@
   "locationUpdated": "Stock location updated",
   "@locationUpdated": {},
 
+  "login": "Login",
+  "@login": {},
+
+  "loginEnter": "Enter login details",
+  "@loginEnter": {},
+
+  "loginEnterDetails": "Username and password are not stored locally",
+  "@loginEnterDetails": {},
+
   "link": "Link",
   "@link": {},
 
@@ -795,6 +804,9 @@
   "profileDelete": "Delete Server Profile",
   "@profileDelete": {},
 
+  "profileLogout": "Logout Profile",
+  "@profileLogout": {},
+
   "profileName": "Profile Name",
   "@profileName": {},