Add some ssl support

[phpmaps]

This PR adds some SSL support to make the CLI a little more secure :)

With Basic Authentication set on an HTTPS WebDav server like: https://bla:bla@webdav.geo.com/bucket the following exception would be raised by the node-fetch module during file transfer.

Error

FetchError: request to https://bla:bla@webdav.geo.com/bucket/test.txt failed, reason: unable to verify the first certificate
    at ClientRequest.<anonymous> (/Users/bla/webdav-watch/node_modules/node-fetch/lib/index.js:1461:11)
    at ClientRequest.emit (events.js:200:13)
    at ClientRequest.EventEmitter.emit (domain.js:471:20)
    at TLSSocket.socketErrorListener (_http_client.js:410:9)
    at TLSSocket.emit (events.js:200:13)
    at TLSSocket.EventEmitter.emit (domain.js:471:20)
    at emitErrorNT (internal/streams/destroy.js:91:8)
    at emitErrorAndCloseNT (internal/streams/destroy.js:59:3)
    at processTicksAndRejections (internal/process/task_queues.js:84:9) {
  message: 'request to ' +
    'https://bla:bla@webdav.geo.com/bucket/test.txt failed, ' +
    'reason: unable to verify the first certificate',
  type: 'system',
  errno: 'UNABLE_TO_VERIFY_LEAF_SIGNATURE',
  code: 'UNABLE_TO_VERIFY_LEAF_SIGNATURE'
}

This PR includes new proposed usage:

Commands

webdav-watch watch --folder ./music --s false --remote https://bla:bla@webdav.geo.com/bucket

OR

webdav-watch watch --folder ./music --ssl false --remote https://bla:bla@webdav.geo.com/bucket

AND

webdav-watch watch --folder ./music --s true --remote https://bla:bla@webdav.geo.com/bucket

OR

webdav-watch watch --folder ./music --ssl true --remote https://bla:bla@webdav.geo.com/bucket

Command using config

webdav-watch watch --c ./config.json

Example Configs

{
    "remote": " https://bla:bla@webdav.geo.com/bucket",
    "folder": "./music",
    "ssl": false
}

{
    "remote": " https://bla:bla@webdav.geo.com/bucket",
    "folder": "./music",
    "ssl": true
}

[zemd]

@phpmaps Sorry for sooo long response, for some reason I didn't get any notifications about your participation. If this PR is still valid for you I like your idea, just couple things should be changed and we are good to go.

[zemd]

let's name this option strict-ssl-verification and it's default should be true

[zemd]

Suggested change

	const httpsAgent = new https.Agent({ rejectUnauthorized: false });
	const opts = argv.ssl ? { body: fileContents, agent: httpsAgent } : { body: fileContents };
	const agent = new https.Agent({ rejectUnauthorized: !argv.strictSslVerification });
	const opts = Object.assign({body: fileContents}, argv.strictSslVerification ? {} : { agent });

[zemd]

since we are in nodejs environment, we don't need this dependency

Suggested change

	"inquirer": "^5.1.0",
	"https": "^1.0.0"
	"inquirer": "^5.1.0"