Update item.js

Fix closing tag in doc.
fix typo for <ion-content> close tag
refactor(scrollView): only update DOM on changes

On line 1188 and 1094, only make updates to the content element’s
transform style when there are actual DOM changes that need to be made,
instead of accessing the DOM just to set the same value. Also many
style() updates.
chore(listView): cleanup element references
refactor(headerBarView): find title by class, not h1 tag
chore(listView): deregister listView on destroy
chore(menuToggle): simplify
chore(sideMenuCtrl): cleanup element references

Line 385, clean up content element reference, and many style() updates
chore(sideMenuContent): cleanup element reference

Clean up element reference on line 194, and some style() updates.
refactor(ionicConfig): setup to easily add configs
Merge pull request #2370 from sabrinaluo/master

fix(docs): fix typo on <ion-content> closing tag
Merge pull request #2359 from zhongsp/patch-1

fix(docs): fix typo on <ion-item> closing tag
fix(viewService): Corrects showBack logic

- Corrects the logic used to determine showBack in the event broadcast
  of `$viewHistory.historyChange`
- Registers ion-nav-view with a `$historyId` in order to correctly
  detect back state when element instance is registered

Revert unnecessary change

Remove unnecessary extra test, condense falsy check

Fix unit tests