Add Tags JSON Export plugin
By creating TagsJsonExportPlugin class
create json version of header
Finish the plugin of exporting tags in mods schema, json format
Modify description of Tags Json-Mods Export plugin
Fix the bugs of export plugins
There are two bugs here,
1. The sql string $sql should not have breaklines
2. For every query we need to create a new command, otherwise the query always return the say results

What's more, the try in ExportController.php is there but completely useless because they didn't handle the error at all.
Fix sql bug in CSV export
They were using image_id, which should media_id
Change the strucutre and add instituion name to the json
Query collection name and add it to json data
Add the weight filtering for "tag weight min" and "tag weight sum"
EXPORT - edit text, fix min tag weight filter

To select tags whose tag weight >= user-defined tag_weight_min,
we need to select the HIGHEST weight for a tag (MAX, not MIN)
Merge JSON export feature into development branch

Merge branch 'jack2684-master' into development