Add explicit link-embed controls to the composer (#120)

* Add explicit link-embed controls

* Update the target rez/size of link embed thumbs

* Remove the alert before publishing without a link card

package.json

@@ -37,6 +37,7 @@
     "email-validator": "^2.0.4",
     "he": "^1.2.0",
     "lodash.chunk": "^4.2.0",
+    "lodash.isequal": "^4.5.0",
     "lodash.omit": "^4.5.0",
     "lru_map": "^0.4.1",
     "mobx": "^6.6.1",
@@ -81,6 +82,7 @@
     "@types/he": "^1.1.2",
     "@types/jest": "^26.0.23",
     "@types/lodash.chunk": "^4.2.7",
+    "@types/lodash.isequal": "^4.5.6",
     "@types/lodash.omit": "^4.5.7",
     "@types/react-native": "^0.67.3",
     "@types/react-test-renderer": "^17.0.1",