* Step 1: move electorn into `app/`.
This is to comply with the suggested directory format of
`electron-builder`: https://github.com/electron-userland/electron-builder#two-packagejson-structure
* Step 2: add build directory with icon files for mac / windows
* Step 3: move all development (web) assets into main directory
* Step 4: add `build` namespace to dev `package.json`
* Step 5: move all dev dependencies into dev file and get rid of
old electron packagers in favor of `eletorn-builder`
* Step 6: target build inside `app/` as everything else is excluded at build time
* Step 7: remove old stuff!
* Step 8: update README
* turn off asar for `child_pty`
Fix the error when executing in some none-bash shell(eg. fish):
```
Failed to execute process './scripts/install.sh'. Reason:
exec: Exec format error
The file './scripts/install.sh' is marked as an executable
but could not be run by the operating system.
```
