CSS style for thumbs on special pages

Extension GlobalUsage uses thumbs on a special page.
Special pages have no CSS class mw-content-ltr or mw-content-rtl.
This change adds a default style for magnify and thumbcaption
which gets flipped by the direction of the user interface language.
This default definition gets overwritten by the existing definition
in shared.css based on the content direction:

/**
 * Image captions
 */
/* @noflip */
.mw-content-ltr .thumbcaption {
	text-align: left;
}

/* @noflip */
.mw-content-rtl .thumbcaption {
	text-align: right;
}

/* @noflip */
.mw-content-ltr .magnify {
	float: right;
}

/* @noflip */
.mw-content-rtl .magnify {
	float: left;
}

Bug: 69215
Change-Id: Ia6aa7c896fbedfe40b97af7358c5fa89223251b3
Merge "CSS style for thumbs on special pages"