SortButton directive, based on angular 1.x+ and bootstrap 3.x+

The directive can be used with its name or as an attribute:

<za-sort-button za-sort-type="alpha" 
 za-sort-order-ascending="true"
 za-sort-event="sortEvent(isAscending)" 
 za-btn-class="btn btn-default btn-xs">
 </za-sort-button>

The attributes are as following:

• za-sort-type can either be alpha, numeric or empty to display the corresponding sort glyphicon
• za-sort-order-ascending determines the initial sort order; when it is true, ascending order is assumed; must be present for the time being
• za-sort-event can be a scope function that gets called, whenever the sorter has been clicked, and passed with the current sortOrder; optional
• za-btn-class is a list of preferrably bootstrap classes that can be used for additional styling (e.g. small buttons); the default value is btn btn-default

• has not been extensively tested with older bootstrap releases; but as along as the glyphicons are present, it should work. The same applies to older Angular releases; it should work with Angular 1.0.x as well - keep your fingers crossed.

• as the directive is using the bootstrap-glyphicons (and classes), some recent 3+ version of bootstraps needs to be loaded for the styling; apart from that no additional JS is needed (i.e. no bootstrap JS).

• update build process for minifying angular-js directive... ; uglify does not work. PRs are welcome...