Allow > 2 parameters in string step definitions

The current implementation does not do a global reg ex replace for string step definitions.. This means the maximum number of placeholders could be 1 quoted dollar placeholder and 1 dollar placeholder. You couldn't have 2 dollar placeholders. 

For example the following would happen..

```
'I have "$btnA" and "$btnB" buttons
-> ^I have "([^"]*)" and "(.*)"$ (still works by coincidence)
``` 
And...
```
'I have $countA accounts and $countB projects' 
-> ^I have (.*) accounts and $countB projects$ 
```