Introduce new built-in macros and history functions in order to enhance time-related tracking capabilities for item values.

1. Add macros {ITEM.VALUE.DATE}, {ITEM.VALUE.TIME}, {ITEM.VALUE.TIMESTAMP}, {ITEM.VALUE.AGE}, {ITEM.LASTVALUE.DATE}, {ITEM.LASTVALUE.TIME}, {ITEM.LASTVALUE.TIMESTAMP}, {ITEM.LASTVALUE.AGE}

1. 1. {*.DATE} - the date (YYYYMMDD) when item value was collected
   2. {*.TIME} - the time (HHMMSS) when item value was collected
   3. {*.TIMESTAMP} - the unix timestamp when item value was collected
   4. {*.AGE} - the time elapsed in seconds since item value was collected until macro evaluation
   5. Support in contexts where {ITEM.VALUE} is supported
   6. Support numeric indexes <1-9> in the context of trigger expressions
2. Add history functions:
   1. lastclock(/host/key, <#num<:time shift>>) - returns the timestamp of the Nth most recent item value
   2. logtimestamp(/host/key, <#num<:time shift>>) - returns the log message timestamp of the Nth most recent log item value
      1. calculation of time-shift is based on the item value clock, not on the log message timestamp
   3. firstclock(/host/key, sec<:time shift>) - returns the timestamp of the oldest item value within evaluation period
   4. Examples:
      1. lastclock(/host/key, #2) - returns the timestamp of the 2nd latest value
      2. logtimestamp(/host/key, #3:now-1d) - returns the log message timestamp of the 3rd latest value one day ago
      3. firstclock(/host/key, 30m) - returns the timestamp of the first value within 30m until now