fix expression vocab memory management and incorrect reallocation of aggregates storage

[abalabin-bamfunds]

also fix and add ability to create tables with index to the sys_info example

This PR fixes a problem when having a string-valued expression column on views of tables that frequently update made perspective grow unlimited amount of memory and slow down dramatically with time. While I could not get a test together that would show this clearly, the results of manual testing are below.

Using the updated sys_info example and the JSON pasted below for the "Generated Data" view the observations before the fix looked like this:

after the fix:

JSON:

{
  "version": "4.4.1",
  "columns_config": {},
  "plugin": "Datagrid",
  "plugin_config": {
    "columns": {},
    "scroll_lock": false,
    "edit_mode": "READ_ONLY"
  },
  "settings": true,
  "table": "superstore_4",
  "theme": "Pro Light",
  "title": "Generated Data",
  "group_by": [
    "String 1"
  ],
  "split_by": [],
  "sort": [],
  "filter": [],
  "group_rollup_mode": "rollup",
  "expressions": {
    "S": "concat(\"String 1\", \"String 2\")"
  },
  "columns": [
    "S",
    "Float 2",
    "Float 3",
    "Float 4",
    "Integer 0",
    "Integer 1",
    "Datetime 4",
    "Boolean 0"
  ],
  "aggregates": {
    "Datetime 4": "dominant",
    "S": "any",
    "Boolean 0": "dominant"
  }
}