Alazar fixes and usability improvements

[terrorfisch]

Changes for alazar daq:

• Do not touch the default config when arming a measurement
• Keep current config in a seperate field
• Extend record to a multiple of a configurable value (4KB by default)

[coveralls]

Pull Request Test Coverage Report for Build 2316

• 23 of 32 (71.88%) changed or added relevant lines in 1 file are covered.
• 16 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 79.944%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qupulse/hardware/dacs/alazar.py	23	32	71.88%

Files with Coverage Reduction	New Missed Lines	%
qupulse/pulses/arithmetic_pulse_template.py	16	89.14%

Totals
Change from base Build 2301:	-0.1%
Covered Lines:	7185
Relevant Lines:	8797

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💛 - Coveralls