added fetch snippet

refactored some code

fixed snippet content empty on changed from list

fixed snippet name not updating on list when changed

browser/main/lib/dataApi/fetchSnippet.js

@@ -0,0 +1,21 @@
+import fs from 'fs'
+import crypto from 'crypto'
+import consts from 'browser/lib/consts'
+
+function fetchSnippet (id) {
+  return new Promise((resolve, reject) => {
+    fs.readFile(consts.SNIPPET_FILE, 'utf8', (err, data) => {
+      if (err) {
+        reject(err)
+      }
+      const snippets = JSON.parse(data)
+      if (id) {
+        const snippet = snippets.find(snippet => { return snippet.id === id })
+        resolve(snippet)
+      }
+      resolve(snippets)
+    })
+  })
+}
+
+module.exports = fetchSnippet