Use twilioserverlessrc in TypeScript projects to point at output

[dkundel]

As called out in #465 for TypeScript projects we need to point the Serverless Toolkit against the output folders in dist/functions and dist/assets as opposed to leaving it to the default of functions and assets. Right now this is done in the package.json for the deploy script by using the --functions-folder and --assets-folder in the script. These flags don't get picked up if you run twilio serverless:deploy though. Instead we should modify the .twilioserverlessrc file that gets created to set the values accordingly instead.

Changes required

1. Add a isTypeScriptProject argument to the templateDefaultConfigFile function in /packages/twilio-run/src/templating/defaultConfig.ts
2. Adjust the logic of templateDefaultConfigFile if isTypeScriptProject is true to set "functionsFolder": "dist/functions" and "assetsFolder": "dist/assets" accordingly.
3. Add same isTypeScriptProject as optional argument to writeDefaultConfigFile method and pass to templateDefaultConfigFile
4. Change createServerlessConfigFile function in packages/create-twilio-function/src/create-twilio-function/create-files.js to accept an isTypeScriptProject flag and pass it to writeDefaultConfigFile
5. Change call of createServerlessConfigFile in packages/create-twilio-function/src/create-twilio-function.js to pass isTypeScriptProject by checking for projectType === 'typescript'
6. Remove the now redundant additions to the start and deploy scripts (lines 54-57) from the createPackageJSON method in create-files.js

Acceptance criteria

After the changes were made the following order of commands should work:

twilio serverless:init ts-example --typescript
cd ts-example
npm run build
twilio serverless:deploy

twilio serverless:start should also work out of the box after running npm run build.