Improved (sync/backup) scripts + misc updates

-Added locks to all sync processes (blocks, markets, peers, masternodes) as well as "create backup", "restore backup" and "delete database" functions. This helps prevent problems with syncing data while a backup is in progress for example
-The code to initialize certain database collections on startup was moved into database.js and is now called from restore_backup.js and delete_database.js. This effectively allows the database to be deleted or restored to a completely different backup while the explorer is still running
-Lock functions (create_lock, remove_lock, is_locked) were moved into explorer.js for better reusability and rewriten to be synchronous
-is_locked function now accepts an array of lock files to be able to check for multiple locks in a single call
-remove_sync_message() function was moved into database.js so that restore_backup.js and delete_database.js can also check for and remove the sync msg if it exists
-Useful Scripts section updated in the README to make it clear that the explorer no longer needs to be stopped for these scripts to be run
-Most if not all log messages now start with a capitlal letter

scripts/benchmark.js

@@ -6,9 +6,9 @@ var mongoose = require('mongoose'),
 
 var COUNT = 5000; // number of blocks to index
 
-function exit() {
+function exit(exitCode) {
   mongoose.disconnect();
-  process.exit(0);
+  process.exit(exitCode);
 }
 
 var dbString = 'mongodb://' + settings.dbsettings.user;
@@ -19,9 +19,8 @@ dbString = dbString + "/IQUIDUS-BENCHMARK";
 
 mongoose.connect(dbString, function(err) {
   if (err) {
-    console.log('Unable to connect to database: %s', dbString);
-    console.log('Aborting');
-    exit();
+    console.log('Error: Unable to connect to database: %s', dbString);
+    exit(999);
   }
 
   Tx.deleteMany({}, function(err) {
@@ -40,7 +39,7 @@ mongoose.connect(dbString, function(err) {
             };
 
             console.log(stats);
-            exit();
+            exit(0);
           });
         });
       });