Add validation for brackets in plain metrics and regex error parsing for tagged metrics

[mchrome]

If an incorrect regex is sent to clickhouse, graphite-clickhouse will return 500: Storage error which is not very informative. This PR adds validation before that can happen to avoid making unnecessary requests to clickhouse and makes graphite-clickhouse return an error that explains the reason why.

For plain metrics: check if all brackets are closed correctly within each node of the path.
Example: a.b.c{d,e}}.f would now return 400: query has unmatched brackets

For tagged metrics: parse regex error from clickhouse.
Example: seriesByTag('name=myMetric', 'tag=*abc*') would now return 400: Incorrect regex syntax

[almostinf]

more readable:

if stack[len(stack)-1] != matchingBracket[c] {
    return true
}

stack = stack[:len(stack)-1]

[mchrome]

Done in 38f3ea7