add EsApiManager, modify error pages and minor fixes

pom.xml

src/main/java/org/codelibs/fess/api/es/EsApiManager.java

src/main/java/org/codelibs/fess/app/web/RootAction.java

src/main/java/org/codelibs/fess/app/web/RootForm.java

...codelibs/fess/app/web/admin/system/AdminSystemAction.java

...va/org/codelibs/fess/app/web/admin/system/SystemForm.java

src/main/java/org/codelibs/fess/app/web/cache/CacheForm.java

src/main/java/org/codelibs/fess/app/web/error/ErrorForm.java

src/main/java/org/codelibs/fess/app/web/go/GoForm.java

src/main/java/org/codelibs/fess/app/web/help/HelpAction.java

src/main/java/org/codelibs/fess/app/web/help/HelpForm.java

src/main/java/org/codelibs/fess/app/web/login/LoginForm.java

src/main/java/org/codelibs/fess/app/web/osdd/OsddAction.java

src/main/java/org/codelibs/fess/app/web/osdd/OsddForm.java

.../org/codelibs/fess/app/web/screenshot/ScreenshotForm.java

...n/java/org/codelibs/fess/app/web/search/SearchAction.java

...ain/java/org/codelibs/fess/app/web/search/SearchForm.java

src/main/java/org/codelibs/fess/es/exentity/User.java

...n/java/org/codelibs/fess/mylasta/action/FessUserBean.java

src/main/resources/app.xml