[CALCITE-1369] Add list of Avatica clients to the web site
[CALCITE-1369] Add list of Avatica clients to the web site

Close apache/calcite#281

minji-kim/calcite,apache/calcite,arina-ielchiieva/calcite,minji-kim/calcite,jcamachor/calcite,apache/calcite-avatica,jcamachor/calcite,apache/calcite-avatica,datametica/calcite,minji-kim/calcite,looker-open-source/calcite-avatica,datametica/calcite,looker-open-source/calcite-avatica,b-slim/calcite,jcamachor/calcite,datametica/calcite,vlsi/incubator-calcite,apache/calcite,vlsi/calcite,apache/calcite,xhoong/incubator-calcite,apache/calcite,sreev/incubator-calcite,looker-open-source/calcite,apache/calcite,apache/calcite-avatica,apache/calcite-avatica,joshelser/calcite-avatica,julianhyde/calcite,dindin5258/calcite,looker-open-source/calcite,googleinterns/calcite,dindin5258/calcite,looker-open-source/calcite-avatica,looker-open-source/calcite,sreev/incubator-calcite,googleinterns/calcite,arina-ielchiieva/calcite,b-slim/calcite,joshelser/calcite-avatica,looker-open-source/calcite,looker-open-source/calcite-avatica,looker-open-source/calcite,googleinterns/calcite,googleinterns/calcite,apache/calcite,vlsi/calcite,b-slim/calcite,b-slim/calcite,looker-open-source/calcite,arina-ielchiieva/calcite,dindin5258/calcite,datametica/calcite,julianhyde/calcite,sreev/incubator-calcite,vlsi/calcite,datametica/calcite,googleinterns/calcite,xhoong/incubator-calcite,sreev/incubator-calcite,jcamachor/calcite,b-slim/calcite,minji-kim/calcite,vlsi/calcite,xhoong/incubator-calcite,vlsi/calcite,julianhyde/calcite,julianhyde/calcite,arina-ielchiieva/calcite,xhoong/incubator-calcite,minji-kim/calcite,julianhyde/calcite,vlsi/incubator-calcite,jcamachor/calcite,apache/calcite-avatica,dindin5258/calcite,googleinterns/calcite,julianhyde/calcite,datametica/calcite,looker-open-source/calcite-avatica,vlsi/calcite,jcamachor/calcite,dindin5258/calcite,joshelser/calcite-avatica,dindin5258/calcite,arina-ielchiieva/calcite