Add Hourly frequency to harvest sources

[amercader]

For those who can't wait!

[metaodi]

@amercader Why can you even set the frequency? You need a cronjob anyway, why not control this over cron entirely? We always used it like that. But maybe I'm missing the point...

[amercader]

@metaodi This is the frequency in which new jobs are automatically created. Setting it to "Weekly" will create a job every week without you having to click "Reharvest".

Of course you can set a cron job that does paster harvester job <source_id> every week or whenever you prefer, but it's more convenient to do it on a per source basis via the frontend.

[letmaik]

+1 Would be really useful.

[davidread]

Our instance has 300 harvester sources covering 15000 datasets - I really don't want an hourly option to be offered, so this should be configurable! (Same goes for the 'ALWAYS' option)

While in the area, I'm not a fan of the name 'BIWEEKLY' as it's ambiguous in UK. I'd vote for it being renamed 'FORTNIGHTLY' or 'EVERY 2 WEEKS'.

Comments welcome - the PR is easy.

[letmaik]

"Every 2 weeks", way easier to understand for non-native speakers :)