Major update of a script building ACE html, remove alerts

[malgosias]

This is a major update to create_ace_html_page.py. It should be considered jointly with PR #3 which contains a new radalerts package for radiation alerts.

This code reads MTA's 12h ACE archive, extracts the last 2 hours of data, computes stats such as average, min and fluence in each channel, and creates MTA's ACE page at

https://cxc.cfa.harvard.edu/mta/RADIATION_new/ACE/ace.html

The result of the code updated in this PR can be viewed at

https://cxc.cfa.harvard.edu/mta/RADIATION_new/ACE/test_dir/ACE/ace.html

Main updates:

• Removed code that sends ACE P3 fluence alert and P5/P6 alert - the alerts will run from a separate script as an independent cron job
• Used astropy Table to read in the data and perform data manipulation
• Added option to pass directory names as arguments instead of reading the house keeping dir list from a file; this makes it easier to e.g. set up test directories

This code can be further improved by reading the data from the ACE.h5 archive generated by Replan Central. This would allow to discontinue MTA's ACE jobs that fetch and store the same ACE data as Replan Central (providing other groups do not rely on ACE files generated by MTA).

Note that ACE P3 fluence alert is still running as part of older bash/awk space weather scripts (which we want to discontinue). P5/P6 alert is not actionable, it only means that the P5 and/or P6 data are not valid and will not be implemented in radalerts.