Create logic for overall timeline size calculation

[theory-of-evrth]

Using Timeline and Node model classes:

• Node - get the earliest and the latest Milestone
• Timeline - of all Nodes, find the earliest and latest points, return node width accordingly

indications: Timeline.getWidth() (not static)

Optional - ask the teacher whether it would be a better practice to return simply start/end dates and calculate exact width in javascript later (it very likely will)

[theory-of-evrth]

there was no need to ask, it is javascript's job and model should not get involved

[theory-of-evrth]

there is no need to have a separate function for that, we can do relative node size and it will be adjusted with milestone placement function