fixing npe in thememgt

git-svn-id: https://svn.wso2.org/repos/wso2/carbon/platform/trunk@182262 a5903396-d722-0410-b921-86c7d4935375
Fixed indexing delay introducing worker pool for indexing and optimize the solrconfig.xml

git-svn-id: https://svn.wso2.org/repos/wso2/carbon/platform/trunk@182265 a5903396-d722-0410-b921-86c7d4935375