Specify number of posts from within the theme JS

[code-with-sam]

Currently the post_limit is set in finally-core.js module and therefor can not be differentiated between different theme. (https://github.com/code-with-sam/finallynetwork/blob/master/platform/src/js/modules/finally-core.js#L11)

Move to default value, that allow customisation.

Need to look at the best way to search/select posts when also filtering hashtags.