Set a flag variable that indicates Electron use

This will enable us to do certain things differently in the Electron
version of MetagenomeScope (e.g. interact with Node.js' sqlite3
module instead of sql.js), without having to actually modify the JS
code between the versions.

The variable's name is METAGENOMESCOPE_ELECTRON_BEING_USED, for
reference.

An aside, which I already sort of knew about but realized more
clearly as I read up on global variables in JS: using globals as much
as MetagenomeScope's viewer interface does is not a good idea! It
looks like the general solution for web apps which have to maintain
least some persistent storage in a page instance is to create a
namespace (which is, itself, a JS object that is a single global
variable), and then just declare every global variable as an attribute
of that object. That way, the only namespace collision we'd need to
worry about would be the main namespace name.

This isn't a significant problem now, but it's worth registering
as its own issue. So I'm gonna go do that.

minify_files.fish

@@ -91,6 +91,12 @@ sed -i'' 's/\(src\|href\)=\([\"\']\)\(js\|css\)\//\1=\2\.\.\/viewer\/\3\//g' ele
 # and we don't have bubble.ico in the electron/ folder anyway
 sed -i'' 's/<link rel=\"shortcut icon\" href=\"bubble\.ico\">//' electron/index.min.html
 
+# Step 4: Set a global flag variable that lets my JavaScript code in xdot2cy.js
+# know that Electron is being used (so that it can do certain things).
+# The question marks allow for some variability in how the <script> is
+# minified.
+sed -i'' 's/window\.METAGENOMESCOPE_ELECTRON_BEING_USED \?= \?0;\?/window\.METAGENOMESCOPE_ELECTRON_BEING_USED = 1;/' electron/index.min.html
+
 # Finally, print ending messages
 echo "File minification complete."
 echo "Make sure that the version of index.min.html you're uploading somewhere is renamed to index.html in its new location."

viewer/index.html

@@ -49,6 +49,10 @@
              will mess up the Electron version HTML generation.
         -->
         <script src='js/jquery-3.2.1.min.js'></script>
+        <!-- The following variable declaration will be modified by
+             minify_files for the Electron version HTML.
+        -->
+        <script>window.METAGENOMESCOPE_ELECTRON_BEING_USED = 0;</script>
         <script src='js/cytoscape.min.js'></script>
         <!-- NOTE if including Cytoscape.js layout plugins for testing, those
              can go here -->