Use correct capabilities

[PhMemmel]

The external functions currently are not checking the necessary capabilities. There are some checks later on, but it should be reworked like this:

• Directly after validating the context in the external function there should be the appropriate capability check, this will usually be require_capability('mod/mootimeter:view', $modulecontext);
• The enrol check like classes/local/pagelist.php:72 will not be needed anymore and should be removed
• Check these for all external functions

[PhMemmel]

Added capability check for mod/mootimeter:view on all external functions and removed the enrol checks with 33484b0

Moving all cap checks to the upper level of the external functions is still a todo.