renamed ActionRouter::checkPermissions to checkPreconditions

As discussed in #1933

feat: add a simple unparser for parsed search queries

To allow creating links with manipulated versions of the current search
query an unparser is necessary. However, the current output of ft_queryP

feat: add a simple unparser for parsed search queries

To allow creating links with manipulated versions of the current search
query an unparser is necessary. However, the current output of ft_queryParser
makes some advanced features hard to detect. Therefore the new
ft_queryUnparser_simple cannot handle negated phrases and `OR` searches.

It should still cover 98% of search queries.

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use expectException instead of setExpectedException for PHPUnit

remove createMock & createPartialMock polyfill, dropping support for PHPUnit 5.7-

Refactored section edit

The data for the section edit button is now passed as an assoziative array which is
encoded in the '#<!-- EDIT(.*) -->#' placeholder as an JSON array.

add tests to DifferenceEngine and optimize each removal in it

fix: prevent two selected options, b/c apparently 'String' == 0 ��

There was a bug, where the options array ['Auto', 0, 1] would result in
HTML option tags where both the 'Auto' and the 0 option we

fix: prevent two selected options, b/c apparently 'String' == 0 ��

There was a bug, where the options array ['Auto', 0, 1] would result in
HTML option tags where both the 'Auto' and the 0 option were selected.

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fix file name
closes #2129

proper handling of "0" as a search query in media manager + test case for this

create some unit tests that test searching in media manager

test: add tests for the section edit regex

reworked notifications to the test system

No globals required anymore, somewhat more general approach to sending
data to the test system. Clean access through keys.

no need for a global output buffer

clean up of the TestRequest object

reformatting
fixing of doc blocks
making internal vars protected

move test page somewhere else to not interfere with other tests

another go at working around the networink troubles at travis #2109

adjusted the tests

Test code for workflow 'show - sectionedit - save/cancel' (with modifications in test classes and 'send_redirect()' and 'act_dispatch()'.

show more info on failed HTTP requests

hopefully this will help with figuring out why our HTTP tests sometimes
fail on travis.

some cleanup fpr set_metadata test

added one more test for internal links

just to be sure, we're not breaking something simple here.

parsertests: replaced var keywords and added type hints

Add tests for array_replace part of set_metadata

response on review

response on review