Add support for form submissions (#780)

* Add support for form submissions

* Make mkdirp async

* Dev: Send forms data to submission-created function

* Delete forms.js

* Use this.error and this.log

* Add mkdirp as dev dep

* A better check for form mime

* Dont trigger form handler on internal URl's

* Fix 'referrer' field in forms

* Normalize multipart form data

* Add convenience fields for forms

* Make form handler function URL relative to root

* Add 'site' field to form event

* Add files to Form event

* Move handleFormSubmission outside

* Formatting

* Remove debug logs

* Fix query params when handling forms

* Add submission-created handler for tests

* Add tests for Netlify Forms

* Formatting

* 🎨 Use non-arrow function

* Fix Node 8 incompatiblity

package.json

@@ -86,6 +86,7 @@
     "cli-ux": "^5.2.1",
     "concordance": "^4.0.0",
     "configstore": "^5.0.0",
+    "content-type": "^1.0.4",
     "cookie": "^0.4.0",
     "copy-template-dir": "^1.4.0",
     "debug": "^4.1.1",
@@ -102,7 +103,7 @@
     "gh-release-fetch": "^1.0.3",
     "git-repo-info": "^2.1.0",
     "gitconfiglocal": "^2.1.0",
-    "http-proxy": "^1.17.0",
+    "http-proxy": "^1.18.0",
     "http-proxy-middleware": "^0.20.0",
     "inquirer": "^6.5.1",
     "inquirer-autocomplete-prompt": "^1.0.1",
@@ -120,6 +121,7 @@
     "log-symbols": "^2.2.0",
     "make-dir": "^3.0.0",
     "minimist": "^1.2.5",
+    "multiparty": "^4.2.1",
     "netlify": "^4.3.1",
     "netlify-redirect-parser": "^2.5.0",
     "netlify-redirector": "^0.2.0",
@@ -133,6 +135,7 @@
     "precinct": "^6.1.2",
     "prettyjson": "^1.2.1",
     "random-item": "^1.0.0",
+    "raw-body": "^2.4.1",
     "read-pkg-up": "^6.0.0",
     "require-package-name": "^2.0.1",
     "resolve": "^1.12.0",
@@ -171,7 +174,7 @@
     "husky": "^3.0.3",
     "lint-staged": "^9.2.1",
     "markdown-magic": "^0.1.25",
-    "mkdirp": "^0.5.1",
+    "mkdirp": "^1.0.4",
     "mocha": "^6.2.0",
     "nock": "^10.0.6",
     "npm-run-all": "^4.1.5",