support per project history override properly

[vladak]

While working on the annotation cache, I noticed a fair bit of confusion/deficiency in the code when handling history related tunables. Specifically, there are 2 problems:

1. confusion between general history and history cache
2. lack of per-project/repository override

For the former, there are pieces of code exhibiting confusion what is historyEnabled and useHistoryCache. Plus related naming problems - Configuration using historyCache boolean while RuntimeEnvironment wrapping that as useHistoryCache(). When fixing that, one would need to tread lightly because this tunable is serialized into configuration.xml.

The history -> history cache dependency should be maintained.

For the latter, the global setting is often checked before descending into code that performs per-repository tunable checks such as

opengrok/opengrok-web/src/main/webapp/minisearch.jspf

Lines 38 to 41 in 05f9a7f

	if (cfg.getEnv().isHistoryEnabled()) {
	if (!cfg.hasHistory()) {
	%><li><span id="history"></span><span class="c">History</span></li><%
	} else {

It should be possible to have history disabled on the global level while overriding it on per-project/repository level. This sort of global bracketing prevents that.