Hotfix for HTTPS and departure station for walking

[GHLasse]

Several changes to address issues:

1. Changed http to https for all google icons (and tested that this works) -> should solve Issue #12
2. Added global variable for last arrival stop so that any walking step will display where to walk from -> solves issue #20
3. Modified style file (and remembered to change the .less as well) so that the icons are same size as the rest of the text (I always had this change done but must have forgotten to upload it) -> as an old fix to improve the style as discussed in #6
4. Took the liberty to make the API key default to

var config = {
...
    apiKeys: {
        google: 'YOUR_API_KEY'
    },
...
}

  this allows one to keep the code cleaner if running multiple instances of MMM-LocalTransport. It's fully optional though - i.e. backward compatible!

[GHLasse]

@CFenner don't mind my bad coding style: the == should obviously be === and I also left some dead code in the .css when merging BUT good news is I tested everything :-D

[GHLasse]

Further changes to address issues and add functionality:

• fixed bug where walking origin was copied from one leg to another (Issue #20)
• Added option to link this module to the calendar module as described in issue #22.
• Added option to display duration for alternative means of transport (walking, cycling, driving)
• fixed as many codeclimate complains as reasonable (the last 9 I think are so minor that it's a hassle to change the code but there are no benefits gained from doing so)
• updated readme file to represent these changes. Though previews of the new functionalities are missing.