standardising all assignment types

[Janther]

After working on #1436 I noticed how there are 4 ways to assign a value to a variable and in each one we have slightly different logic.

// Constant Definition
uint constant FOO_BAR = 0x1234;

contract Foo {
    // State Variable Definition
    uint foo = 0x1234;

    function bar() {
        // Variable Declaration
        uint foobar = 0x5678;

        // Assignment Expression
        foobar = 0xabcd;
    }
}

This is a debt we had since the ANTLR parser.

This PR aims to standardise all of these ways to format the right side of the assignment operator. We did stay as close as possible to the way Prettier formats as well.

[fvictorio]

This looks good to me, but we should make this a minor release, and clarify in the release notes that there are formatting changes in the name of consistency.