Use appname property as title for index.html page. Closes #66

This PR proposes to use the  `<%= appname %>` property as value for a generated `index.html` `title` tag. This will fully meet the issue main request I believe.
This PR uses solution based on `generator-webapp` solution trying to keep in line with other solutions in Yeoman family:
http://git.io/tQTwwQ
Other Yeoman generators either do not set title value at all (most of them I think) - contrary to this generator.

Generated titles:
```json
"name": "app-polymer"
```
```html
<title>app polymer</title>
```
```json
"name": "mypolymerapp"
```
```html
<title>MyPolymerApp</title>
```
 
```
Uses the application name property as the title of a generated
index.html document. Based on generator-webapp solution:
http://git.io/tQTwwQ
```

tests:
https://gist.github.com/peterblazejewicz/2743b387be412faa3ef1