Implement new rules for further conformity checking

[jaymcp]

This PR adds several new rules that will help us with common code smells:

• Use statements A-Z
  • must be in alphabetical order
    • SlevomatCodingStandard.Namespaces.AlphabeticallySortedUses
• No unused use statements
  • for if a namespace is being imported, but is not referenced
    • SlevomatCodingStandard.Namespaces.UnusedUses
• No use statement grouping
  • no use Namespace\{Sub_NS_One,Sub_NS_Two}\Foo
    • SlevomatCodingStandard.Namespaces.DisallowGroupUse
• Strict equality
  • will shout at you for == or !=
    • SlevomatCodingStandard.Operators.DisallowEqualOperators
• No increment/decrement
  • will shout at you for $i++ or $i-- (instead of $i += 1 or $i -= 1)
    • Squiz.Operators.IncrementDecrementUsage
    • SlevomatCodingStandard.Operators.DisallowIncrementAndDecrementOperators
• Generics for array type hints
  • use array<int,string> instead of string[]
    • SlevomatCodingStandard.TypeHints.DisallowArrayTypeHintSyntax
• Shorthand scalars
  • int and bool instead of integer and boolean in type hint comments (we already have this for the actual type hints)
    • SlevomatCodingStandard.TypeHints.LongTypeHints
• Nullable in type hints
  • will flag when a param has int $foo = null but comment type hint is not nullable
    • SlevomatCodingStandard.TypeHints.NullableTypeForNullDefaultValue
• No variable variables
  • disallows $$foo
    • SlevomatCodingStandard.Variables.DisallowVariableVariable
• No unused variables
  • self explanatory
    • SlevomatCodingStandard.Variables.UnusedVariable
• No useless variables
  • this will throw when a variable is assigned and then returned
    • SlevomatCodingStandard.Variables.UselessVariable