Added possibility to enter past date in /spend command to log time in the past

What does this MR do?

Provides feature to enter date in /spend command to logging time in the past. In UI there was added date when time was spent like on a screenshot. Example: '/spend 10m 2017-02-02'. Acceptable formats of date: long: YYYY-MM-DD, short: YY-M-D or mixes of this. Acceptable delimiters: '-' '/' '.' and few variants of delimiters mixes but i highly not recommend this

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

Issue #1312