Upgrade wrt for electron v1.6.7

Upgrade wrt for electron v1.6.7

The wrt was built on electron v0.35.4 and
the electron has been upgraded to v1.6.7.

There are following differences between them.
This upgrades the changed APIs for electron v1.6.7.

1) requiring electron module

The usage of electron module has been changed.
For instance, |const app = require('app')| is changed to
|const {app} = require('electron')|.

2) ipc usage

The ipc has been separated to ipcMain and ipcRenderer.
The related changes are applied by this.

Also, this revises the message types as ipc_message or was_event.
The ipc_message communicates between different processes
but was_event communicates in same process.

Change-Id: I8e6467a7721d9b715c918ccb179a3fe461ddbea4
Signed-off-by: Youngsoo Choi <kenshin.choi@samsung.com>