Add defaults parameter to one of the Testing.Browser contructors

the new parameters allows for passing default browser context setting
through all calls on browser instance
move code around a bit in BrowserDefaultsFixture
Add BrowserContext defaults parameter to the other Testing.Browser constructor
add test for passing context both via ctor and call
fix spelling
Use DefaultContext method to initialize defaultContext field
comply to human style cop
Fixing fixture formatting

Spell given correctly
Newlines before GWT comments
Merge pull request #1419 from horsdal/testing-defaults-3

Add ability to pass in browser context defaults to Testing.Browser