* Commit 5df675a (fix demo/outside legend bug and null data autoscale
  bug) introduced a guard in plotAutoSize to avoid calling layoutStyles
  while autosize is set to 'initial'.

* Commit ee974d9 (autosizing in shareplots, autosize aspect ratio
  restrictions and ...) removed the call to layoutStyles but forgot to
  remove the guard.

* This commit removes the guard.

* Checked that all the jasmine and image tests still pass.

* Moved initial call to `plotAutoSize` into `Plots.supplyDefaults(gd)`.

* Replaced `{ autosize: 'initial' }` with the flag
  `gd._fullLayout._initialAutoSizeIsDone`.

* `{ autosize: false }` the values of width and height undefined in
  `gd.layout` will be autosized only once.

* `{ autosize: true }` only autosizes the values of width and height
  undefined in `gd.layout`.

Fixes plotly#537

* Previous image didn't honour the width and height set in the layout.

* Added test to check `Plotly.newPlot` respects `layout.width` and
  `layout.height`.

* Fix bug in `plotAutoSize`, triggered when `autosize` and `frameMagins`
  are both enabled and `gd` is a plain object.

* Ensure `autosize` doesn't set values of width and height smaller than
  the minimum defined in the corresponding layout attribute.

* Do not do the initial autosize if both config.autosizable and
  layout.autosize are false.

* Fix bug introduced in the commit for respecting `config.autosizable`.

* Initialise `layout.width` and `layout.height` if `autosize` is false.