Score file reading: fix bar line span for non-5-line staves.

While reading a score, if a staff is found with number of lines != 5 and no explicit bar line span set (i.e. default bar line span), the bar line span remains set as for a 5-line staff.
fix #21168
Fix StaffType::operator==

For TAB_STAFF_GROUP, the equality operator does not check all the member variables (does not call isSameStructure())

Also, simplified some duplicate tests.
fix #12112
fix 'German accent'
ignore some backup- and temp. files

created by vim and QtCreator
fix stray rest
add a comment

same as the one in the correspoding .h file
make it C++ and don't translate

translating doesn't work (not this way at least) and won't happen anyway
as the translation mechanism is set up only later in the code, after the
use of the usage() function.
Remove the mention of an option that (no longer?) exists
fix #25755: avoid duplicates in plugin help

and add two missing ones. Also remove a 'plugin comment' from a .cpp
file, where it doesn't serve any purpose anyway (but at first tricked me
into believing this were the the culprit for the duplicate)
improve mtest

unified diffs are much easier to read
update file format history

as per http://musescore.org/en/developers-handbook/version-information
small optimization: call spatium() only once

and fix indentation
improve builtin plugin documentation

reformatting, removing some comments that are irrelevant to plugin
framework in a way that DoxyGen should still find them, documenting the
enums and fully qualify all types that are specific to MuseScore,
remove/add some semicolons

which QtCreator's syntax check complains about (but not the compiler)
remove some apparently unndeeded Q_ENUMS()
expose HairpinType, Syllabic and GlissandoType

as the only Q_ENUMS() not accompnied by corresponding a
Q_DECLARE_METATYPE()
fix #21999
change velocity according to value defined in instruments.xml
leftover improvements to plugin documentattion...