Fix dejittering of timestamps

[cbrnr]

Fixes #163. The problem was that streams marked as can_drop_samples (e.g., video) were not excluded from dejittering, which is what happens in the MATLAB implementation.

[cbrnr]

@magdabiadala I've tested the fix with your example file and I get approximately the same start times for all streams now:

Stream 4 (PolarBand): 19263.77, 19263.78, 19263.79, 19263.79, 19263.80, 19263.81, 19263.82, 19263.82, 19263.83, 19263.84
Stream 6 (Shimmer_GSR): 19264.30, 19264.32, 19264.34, 19264.36, 19264.38, 19264.40, 19264.42, 19264.44, 19264.46, 19264.48
Stream 2 (HMD): 19264.29, 19264.30, 19264.31, 19264.32, 19264.33, 19264.34, 19264.35, 19264.37, 19264.38, 19264.39
Stream 5 (ViveProEye): 19270.96, 19271.06, 19271.07, 19271.08, 19271.09, 19271.10, 19271.15, 19271.20, 19271.26, 19271.31
Stream 3 (LookedAtObject): 19272.27, 19272.28, 19273.45, 19273.46, 19273.55, 19273.56, 19273.58, 19273.59, 19273.60, 19273.62
Stream 1 (ExperimentMarkerStream): 19267.14, 19268.13, 19271.05, 19331.73, 19354.02, 19405.50, 19406.51, 19418.08, 19469.14, 19477.32

Previously, the first 10 timestamps in streams 2 and 5 were shifted by around 47s:

Stream 2: Calculated effective sampling rate 70.1133 Hz is different from specified rate 90.0000 Hz.
Stream 5: Calculated effective sampling rate 70.0808 Hz is different from specified rate 90.0000 Hz.
Stream 4 (PolarBand): 19263.77, 19263.78, 19263.79, 19263.79, 19263.80, 19263.81, 19263.82, 19263.82, 19263.83, 19263.84
Stream 6 (Shimmer_GSR): 19264.30, 19264.32, 19264.34, 19264.36, 19264.38, 19264.40, 19264.42, 19264.44, 19264.46, 19264.48
Stream 2 (HMD): 19217.11, 19217.12, 19217.13, 19217.15, 19217.16, 19217.18, 19217.19, 19217.21, 19217.22, 19217.23
Stream 5 (ViveProEye): 19221.51, 19221.52, 19221.54, 19221.55, 19221.57, 19221.58, 19221.60, 19221.61, 19221.62, 19221.64
Stream 3 (LookedAtObject): 19272.27, 19272.28, 19273.45, 19273.46, 19273.55, 19273.56, 19273.58, 19273.59, 19273.60, 19273.62
Stream 1 (ExperimentMarkerStream): 19267.14, 19268.13, 19271.05, 19331.73, 19354.02, 19405.50, 19406.51, 19418.08, 19469.14, 19477.32