quakeml: fix helper method to write time to xml, was disregarding
microseconds, simply relying on `UTCDateTime.__str__` is totally fine
quakeml: write amplitudes to quakeml + basic test
flake8
flake8
flake8: some update in flake8/pyflakes in travis makes it complain about
comments that start with no space after the hash sign. we have roughly
700 appearances of that. while this is indeed ugly and should be fixed,
it's too much ado right now (and would be a crazy ammount of work with
merging into master...), so for now just ignore this.
Merge remote-tracking branch 'upstream/releases'

Conflicts:
	obspy/core/util/testing.py
	obspy/fdsn/client.py
	obspy/imaging/scripts/mopad.py
	obspy/xseed/tests/test_blockettes.py
	obspy/y/core.py
fix flake8 commit
Merge remote-tracking branch 'upstream/releases'
Merge remote-tracking branch 'upstream/releases' into fix_qml_amplitudes
Merge remote-tracking branch 'upstream/master' into quakeml_namespaces
update quakeml xsd
Merge remote-tracking branch 'upstream/releases'
fix missing errors for period element of amplitude
Merge remote-tracking branch 'upstream/releases' into fix_qml_amplitudes
adapt some quakeml test files

only cosmetic changes, easier to modify the test file than adapt testing routine
flake8
Merge remote-tracking branch 'upstream/master' into quakeml_namespaces
bug fixes in quakeml Amplitude I/O

triggered by a suddenly failing mchedr test (writing to quakeml.
@claudiodsf: beware that anything so far converted from mchedr to
quakeml got stripped of amplitudes during conversion!)
quakeml: don't fill in empty WaveformStreamID (but None) during parsing
Merge pull request #763 from obspy/fix_qml_amplitudes

QuakeML misses I/O for Amplitude(s)