Remove EPHIN msids and facilitate arc and snapshot decoupling

[malgosias]

This PR removes 3 MSIDs related to EPHIN temperature from the snap display: "Ephin Temp", "EIO Temp", "Eph temp", and adds a functionality to write Chandra snapshot in the json format to remove Replan Central dependency on the chandra.snapshot layout changes.

Affected files: snap_format.pm, tlogr_linux.pl. The new layout can be inspected on BUOCC Snapshot on luke-v. The code change was tested on old telemetry and produced the following chandra.snapshot layout differences:

...
Pitch Mom. 2.251 SCS 132 ACT Warm Rad -79.6
Yaw Mom. -17.247 SCS 133 ACT RadMon ENAB
PMTANKP 118.159 SCS 107 INAC
...

to be compared with

...
Pitch Mom. 2.251 SCS 132 ACT Ephin Temp 0.0000 Warm Rad -79.6
Yaw Mom. -17.247 SCS 133 ACT EIO Temp 0.0000 RadMon ENAB
PMTANKP 118.159 SCS 107 INAC EPH temp 115.28
...

The chandra.snapshot.json file is formatted as follows:

{MSID1: {"time": ..., "value": ..., "status": ...}, MSID2: {"time": ..., "value": ..., "status": ...}, ...}


[taldcroft]

Output this time as a string in the standard YYYY:DOY:HH:MM:SS.sss format so there is no ambiguity in interpretation by downstream apps.