Add window restore icon

[csnewman]

When maximised, the icon to de-maximise the window is displayed as the maximise icon.

Current:

Expected:

[EriKWDev]

A tutorial for how to achieve this look in electron (here) mentioned some svg icons from a pull-request that was rejected.

Don't know where the original author got it from, but here is the svg for the restore button:

<svg width="11" height="11" viewBox="0 0 11 11">
    <path d="m11 8.7978h-2.2021v2.2022h-8.7979v-8.7978h2.2021v-2.2022h8.7979zm-3.2979-5.5h-6.6012v6.6011h6.6012zm2.1968-2.1968h-6.6012v1.1011h5.5v5.5h1.1011z" stroke-width=".275" />
</svg>

[esDotDev]

I have a PR here that adds this Icon, just not quite sure how to wire it up: https://github.com/bitsdojo/bitsdojo_window/pull/22

The PR moves away from SVG, as the line rendering is harder to control and can easily create aliased results.

[ankushmishra2903-official]

I found solution in #114 just create my own button