Abbreviate WebDriver configuration property browserCapabilities as browser

Story:

In order to save typing and make the WebDriver configuration more readable
As a tester
I want to be able to configure the browser using the property name "browser" instead of "browserCapabilities"

Scenarios:

Given I want to use the FirefoxDriver when running my Drone WebDriver tests
When I set the browser (e.g., firefox) in the WebDriver configuration property named "browser"
Then Drone should interpret the value of that property as the browserCapabilities
; And Drone should select and initialize the FirefoxDriver
; And Drone should inject the FirefoxDriver into the @Drone injection point in the test

Given I want to use the FirefoxDriver when running my Drone WebDriver tests
: And I have an existing Drone WebDriver configuration
When I set the browser (e.g., firefox) in the WebDriver configuration property named "browserCapabilities"
Then Drone should interpret the value of that property as the browserCapabilities
; And Drone should select and initialize the FirefoxDriver
; And Drone should inject the FirefoxDriver into the @Drone injection point in the test

Rationale:

While browserCapabilities is the official name for specifying the browser by its coordinates name, version and platform, we need not expose this formality to our users. We can honor both names for this property, perhaps throwing an exception if both are present. Once we sort that out, we should propose another scenario to cover it.