Change list_assets API limit to 101

[abitmore]

It's not convenient to fetch next page with the 100 limit, although not impossible.

See code:

      /**
       * @brief Get assets alphabetically by symbol name
       * @param lower_bound_symbol Lower bound of symbol names to retrieve
       * @param limit Maximum number of assets to fetch (must not exceed 100)
       * @return The assets found
       */
      vector<asset_object> list_assets(const string& lower_bound_symbol, uint32_t limit)const;

Need to change code and doc.

Related: bitshares/bitshares-ui#1435

[abitmore]

Done with #872.