Add the ability to customize index.html (#113)

User may provide a custom index.html template file to be used instead
of the built-in version. Changes to this file are watched by laminard
using inotify in order to load and compress the custom file for gzip
delivery, reusing the existing method for serving static assets.

This feature obviates the custom css feature, so remove references from
the manual and add a deprecation warning if it is used.

Add a section to the UserManual describing how to use this feature and
including a link to an example using Semantic UI.

src/laminar.cpp

@@ -113,6 +113,12 @@ Laminar::Laminar(Server &server, Settings settings) :
       .addPath((homePath/"cfg"/"jobs").toString(true).cStr())
       .addPath((homePath/"cfg").toString(true).cStr()); // for groups.conf
 
+    loadCustomizations();
+    srv.watchPaths([this]{
+        LLOG(INFO, "Reloading customizations");
+        loadCustomizations();
+    }).addPath((homePath/"custom").toString(true).cStr());
+
     srv.listenRpc(*rpc, settings.bind_rpc);
     srv.listenHttp(*http, settings.bind_http);
 
@@ -121,6 +127,14 @@ Laminar::Laminar(Server &server, Settings settings) :
     loadConfiguration();
 }
 
+void Laminar::loadCustomizations() {
+    KJ_IF_MAYBE(templ, fsHome->tryOpenFile(kj::Path{"custom","index.html"})) {
+        http->setHtmlTemplate((*templ)->readAllText().cStr());
+    } else {
+        http->setHtmlTemplate();
+    }
+}
+
 uint Laminar::latestRun(std::string job) {
     auto it = activeJobs.byJobName().equal_range(job);
     if(it.first == it.second) {
@@ -789,8 +803,14 @@ R"x(
     return true;
 }
 
+// TODO: deprecate
 std::string Laminar::getCustomCss() {
     KJ_IF_MAYBE(cssFile, fsHome->tryOpenFile(kj::Path{"custom","style.css"})) {
+        static bool warningShown = false;
+        if(!warningShown) {
+            LLOG(WARNING, "Custom CSS has been deprecated and will be removed from a future release. Use a custom HTML template instead.");
+            warningShown = true;
+        }
         return (*cssFile)->readAllText().cStr();
     } else {
         return std::string();