diffexp performance & UX improvements (#431)

* new diffexp REST API spec

* new diffexp REST API; faster diffexp and dataframe slicing

* first draft of fast diffexp

* convert variance calculation to two-pass method

* lint

* update front-end use of API

* fix typo in spec

* disable content compression

* catch index filter format errors

* clean up of dead code

* resolve PR review comments

client/src/components/geneExpression/index.js

@@ -152,9 +152,9 @@ class GeneExpression extends React.Component {
                     zebra={index % 2 === 0}
                     ranges={d3.extent(values)}
                     isDiffExp
-                    avgDiff={value[1]}
-                    set1AvgExp={value[4]}
-                    set2AvgExp={value[5]}
+                    logFoldChange={value[1]}
+                    pval={value[2]}
+                    pvalAdj={value[3]}
                   />
                 );
               })