Refactored overriding inline styles

[mmrtnz]

• Refactored component inline-style structure.
  • Before components had a get function for each element that had inline-styles. Now, all inline-styles are contained in one function called getStyles(). This change was done to improve readability. Here is an example of what I mean:

// Before
_main: function() {
  return { /* inline styles for main */ };
},

_elementA: function() {
  return { /* inline styles for elementA */ };
},

...


// After
getStyles: function() {
  return {
    root: { /* inline styles for main */ },
    elementA: { /* inline styles for elementA */ },
    ...
  };
}

• Remade merge functions of StylePropable
• Created new utility file called Extend
  • This was taken from ThemeManager's merge function.
  • Similiar to jQuery's extend function

[mmrtnz]

This may resolve #569 #563.