[FEATURE] Add hasSubpages condition ViewHelper

Using this ViewHelper it is possible to add some extra markup to wrap a sub-navigation in without having to use the menu ViewHelper which can be a little overhead.
[TASK] Adapt refactoring of condition ViewHelpers
[TASK]  Guard against empty/zero page UID passed to pageSelect
[FEATURE] Add isString condition ViewHelper
[FEATURE] Add isUppercase condition ViewHelper
[FEATURE] Add isLowercase condition ViewHelper
[TASK] Add renderChildren() to enable inline usage
[FEATURE] Add preg ViewHelper
[BUGFIX] Incorrect class names
[FEATURE] Add isArray ViewHelper
[TASK] Add optional template variable assignment
[TASK] Remove wrong usage of renderChildren in condition ViewHelpers
[FEATURE] Add isNumeric ViewHelper
[FEATURE] Add isFloat ViewHelper
[FEATURE] Add isInstanceOf ViewHelper
[FEATURE] Add isInteger ViewHelper
[FEATURE] Add isObject ViewHelper
[DOC] Impoved wording
[FEATURE] Add isNull ViewHelper
[FEATURE] Add contains ViewHelper