Generalize Modules with assertions

[angrykoala]

Instead of separate modules and assertion modules, make the assertions part of the browser modules. E.g.:

class MyModule extends BrowserModule{
    constructor(browser) {
        this._browser = browser;
    }

    _beforeOpen() {
        // BeforeOpen Hook
    }

    _beforeClose() {
        // beforeClose Hook
    }

   get assertions(){
     // return the assertions object of the module, if any
   }

After the assertions are defined, the assertions module will inject these in the browser.assert[my_module]