Dialog now always full-sized about metro-bootstrap

[Spinarooni]

My original pull request made the change in the bootstrap modal.less file. When it was moved to it's own less file it broke the CSS precedence order. The bootstrap file has:

.modal-dialog {
position: relative;
margin-left: auto;
margin-right: auto;
width: auto;
margin: 10px;
z-index: (@zindex-modal-background + 10);
}

To fix the issue we needed to reset those left and right margins. The modal.less file that was added has:

.modal-dialog {
position: relative;
width: auto;
margin: 30px auto;
z-index: (@zindex-modal-background + 10);
}

width: auto is breaking the width because it's being set later in the CSS precedence order due to where it's being loaded.

I think all we need in modal.less is:

.modal-dialog {
margin-left: auto;
margin-right: auto;
}