Add margins methods taking percentage parameters

[lucdion]

Add margins methods taking percentage parameters:

• marginTop(_ percent: FPercent)
  Top margin specify the offset the top edge of the item should have from it’s closest sibling (item) or parent (container).
• marginLeft(_ percent: FPercent)
  Left margin specify the offset the left edge of the item should have from it’s closest sibling (item) or parent (container).
• marginBottom(_ percent: FPercent)
  Bottom margin specify the offset the bottom edge of the item should have from it’s closest sibling (item) or parent (container)
• marginRight(_ percent: FPercent)
  Right margin specify the offset the right edge of the item should have from it’s closest sibling (item) or parent (container).
• marginStart(_ percent: FPercent)
  Set the start margin. In LTR direction, start margin specify the left margin. In RTL direction, start margin specify the right margin.
• marginEnd(_ percent: FPercent)
  Set the end margin. In LTR direction, end margin specify the right margin. In RTL direction, end margin specify the left margin.
• marginHorizontal(_ percent: FPercent)
  Set the left, right, start and end margins to the specified value.
• marginVertical(_ percent: FPercent)
  Set the top and bottom margins to the specified value.

Usage examples:

  view.flex.margin(20%)
  view.flex.marginTop(20%).marginLeft(20%)
  view.flex.marginHorizontal(10%)