RDISCROWD 5743 task browse bookmarks

[n00rsy]

Issue number of the reported bug or feature request: RDISCROWD-5743

Describe your changes
Add new API methods:

1. GET /<user_name>/taskbrowse_bookmarks/<short_name>: get a list of the user's bookmarks for the specified user and project.
   Response JSON:
   { name1: url1, name2: url2...}

2. POST /<user_name>/taskbrowse_bookmarks/<short_name>: add a new bookmark for the specified user and project.
   Request JSON:
   {name: <new bookmark name>, url: <new bookmark url>}
   Response JSON: new list of bookmarks
   { name1: url1, name2: url2...}

3. DELETE /<user_name>/taskbrowse_bookmarks/<short_name>: delete the specified bookmark by name
   Request JSON:
   {name: <bookmark to delete>}
   Response JSON: new list of bookmarks
   { name1: url1, name2: url2...}

Bookmarks are stored in user data (in postgres db) in the following format:

user.info = { 
             metadata...,
             taskbrowse_bookmarks : {
	                            project_name : {
			                         bookmark_name : url,
                                                 bookmark_name : url,
                                                 bookmark_name : url
                                                 ....
		                    },
	                            project_name : {
			                         bookmark_name : url,
                                                 bookmark_name : url,
                                                 bookmark_name : url
                                                 ....
		                    }
                                    ...
                  }
}

Testing performed
Tested locally

[coveralls]

Pull Request Test Coverage Report for Build 4555766290

• 70 of 70 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 94.094%

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Totals
Change from base Build 4545768309:	0.02%
Covered Lines:	16809
Relevant Lines:	17864

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💛 - Coveralls

[dchhabda]

lgtm. can be merged upon tests/coverage pass. Thanks!