Move buildings layer to fix associated issues

[jragusa]

The rendering of underground building #552 raises the question of the relative position of the buildings layer which is also discussed in several others issues:

• Building doesn't render on top of highway areas any more #688 with regard highways
• railway=platform rendered over building=roof #2037 and Wrong colour for oneway arrow on path with bicycle=designated  #2054 with regard to railway=platform
• Render building=roof differently to expose underlying features #2475 about building=roof
• render military areas and prisons on top of buildings and roads #1285 with regard to military overlay and prison pattern (see comment)

Resolving one after one each of these problems will lead to continuous corrections of the layers with respect to the buildings one. So, we need to discuss what would be the correct position of the buildings layer to fix in one shot all of these problems.

Basically, we need to move stations-poly and all highway related layers before (e.g. below) buildings layer but what about underground building in this case ? There is also some aside problems such as the lack of rendering of roof parking (only icon is rendered).

[jeisenbe]

Closing this meta-issue; see linked issues for more specific discussion: #688 (highway areas)
#1285 (military and prison overlays)
#2037 and #2054 (railway=platform), #2475 (building=roof)