Optionally set the sticky-header attribute for main buefy grids

should affect the 'index' and 'view' (with rows) but i don't think any
other pages will get this..?

tailbone/templates/grids/buefy.mako

@@ -140,6 +140,14 @@
        :loading="loading"
        :row-class="getRowClass"
 
+       ## TODO: this should be more configurable, maybe auto-detect based
+       ## on buefy version??  probably cannot do that, but this feature
+       ## is only supported with buefy 0.8.13 and newer
+       % if request.rattail_config.getbool('tailbone', 'sticky_headers'):
+       sticky-header
+       height="600px"
+       % endif
+
        :checkable="checkable"
        % if grid.checkboxes:
        :checked-rows.sync="checkedRows"